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H: Quadcopter return to home function not working
I have a small S49 quadcopter. Whenever I am flying it and initiate Return to Home on the controller, it always returns to the wrong location compared to where it launched from. Sometimes maybe 5/10 metres away. How can this be fixed?
AI: Having Googled the S49 drone, it appears that your drone uses ‘headless rth’.
This means that instead of using GPS, the drone goes into ‘headless mode’ then pitches backwards towards you.
Unfortunately, due to the nature of how this works and the inaccuracies of the accelerometer, this process is rarely accurate.
I don’t know of any way to fix this as it is a hardware limitation as far as I know, so I suggest you think of it more as a way to move the drone roughly towards yourself to recover it if you lose orientation, rather than a way to have the drone return and land accurately. |
H: Why do multirotors usually have four propellors?
I've observed that hover-capable drones almost always have four propellers. There are helicopters of course, which have two, but in general, the vast majority of UAVs seem to go with four propellers.
It seems to me intuitively that this must be less efficient: More points of friction, more wiring, more weight, etc...
Why is it that we see an overwhelming predominance of four propeller drones rather than, for instance, three propellers? Is it just because it's easier to control or gives a smoother flight? Or is there some physical reason?
AI: With aircraft, there are 6 degrees of freedom (DoF) we want to control (roll-pitch-yaw, and x-y-z), but for hovering vehicles (i.e. rotorcraft) we can get away with controlling two degrees of freedom (x-y) by combining the 4 other degrees (roll-pitch-yaw + z).
There are many ways of controlling those four DoF, typically:
helicopters, which use variable pitch blades and some combinations of main and tail rotors, to result in a combination which results in control over roll, pitch, yaw, and thrust
tricopters, quadcopters, hexacopters, octocopters, etc..., all of which use their blades to control the roll, pitch, yaw, and thrust.
Somewhere it is inescapable that for stabilized flight on all four DoF you must have the ability to control each DoF. Mathematically, the quadcopter provides the lowest number of simple actuators that accomplish the job. Each actuator can work by simply speeding up or slowing down, whereas helicopters and tricopters require some other kind of actuation, usually a complex one. It turns out from a pragmatic viewpoint speeding up and slowing down motors is much more robust than changing angles of spinning blades.
Quadcopter
Formally, it looks like this:
So quadcopters reign over helicopters and tripcoters because they're simple. Each axis is controlled by a certain combination of motor speeds and all axes are independent, i.e. when you increase thrust you don't have to also worry about changing the pitch.
So why not hexas, octos, etc...?
Hexacopters
Hexas can lift more, but provide no additional safety margin because there is no way to stabilize all four axes when an arbitrary motor goes out (there are certain configurations which can continue to fly if one motor out of a set of four fails, but cannot fly if either of the other two fail).
Hexas also are less efficient, since they use smaller propellers. (Without diving into blade theory, and simplifying somewhat, the most efficient blade is a single blade which is infinitely large and moving infinitely slowly.)
Hexas also have 6 motors for four degrees of freedom, so when they're all flat you get what is called an "overconstrained" system. You can actually angle them to interesting effect, e.g. CyPhy Work's LVL 1 drone.
Octocopters
Octos theoretically can continue to fly if any arbitrary motor fails, but in reality, you'll likely encounter blade stalling effects or other pathologies that will not allow the octo to sustain flight. This happens because the typical octo is loaded past the point where 4 motors can carry it safely. However, certain high-value vehicles, such as those carrying expensive cameras, are octos because it's cheaper to over-spec the octo's batteries and motors than it is to replace a $50k camera.
Octos are also less efficient, for the same reason as hexas. |
H: Why does a brushless drone fly longer?
I have noticed that drones with brushless motors fly longer than those with brushed motors. Why are drones with brushless motors able to fly for longer amounts of time?
AI: Brushless motors (aka BLDC) are typically[*] more efficient than brushed DC motors. Higher efficiency equates to longer flight times for a same battery pack.
Amongst other reasons:
The inrush current at the moment of commutation can involve sparks (which is an inefficient waste of energy), and in any case is a free-running operation without the possibility for optimization.
The carbon brushes have a somewhat higher resistance, which is an electrical energy loss
The carbon brushes involve a certain amount of drag, which is a mechanical energy loss
The EM field is not easily controllable to reduce torque ripples, resulting in mechanical energy losses. Anecdotally, you can hear these ripples, especially when comparing power tools using universal motors (i.e. brushed AC wound in series) vs BLDC. Sounds represents energy, all other things being equal a noisier drive is a less efficient drive.
Brushless motors also are easily built into outrunner applications, which is appropriate for high-torque direct drive applications, such as a propeller. An inrunner needs an inefficient gearbox to develop the torque required to spin a blade (which might also be complex, costly, and weighty).
An oftentimes overlooked consequence of brushless efficiency is heat generation. Fundamentally, what limits a motor's power is heat, and producing less of it means that more energy can be supplied from a smaller package. The smaller package means lighter weight, which equates to longer-runtime.
Each of these on its own is small, but summed together they result in a far superior drone operation from brushless than brushed.
[*] There are some extremely efficient (>95%) brushed motors out there. However, the engineering required to get that high efficiency is costly. Cheap mass-produced brushed motors will never have those kinds of tolerances, but brushless motors are much less sensitive to manufacturing imprecision. |
H: ESCs for inverted flight?
What types of brushless drone ESCs are reversible and will work for flying inverted?
AI: ESCs loaded with recent versions of BLHeli (BLHELI_S and BLHELI_32) will support reversible motor direction, either through Dshot commands (obviously only supported when using Dshot signaling) or with zero-throttle centered around the middle throttle position, 1500µs (supports Oneshot/Multishot in addition to Dshot).
These modes can be set up in the BLHELI Suite configurator. |
H: How can I build a drone similar to a DJI Mavic 2?
I want to build a drone with the same functionality as a DJI's Mavic 2. Are there any books/videos/guides available? What would be involved?
I need a flying machine that:
has a good enough camera for short films
has at least 25 mins of flight time
is small and portable
has an object sensing system, so I don't wreck it :)
has a object tracking system to track people, cars, etc...
Its main purpose is "object tracking" for short films.
I know it will not be easy to build, but have the time and money to do it. I just need to know how.
AI: Everything you requested is possible in a home-built unit (EXCEPT: object sensing and tracking.)
I'd recommend the painless360 youtube channel. Lee has detailed build videos on just about every kind of RC model that flies as well as tutorials about radio gear, GPS, ESC, batteries, camera gear, etc. They are excellent and you can follow along with the builds. It makes building your first model a great chance of success. His channel is amazing especially if you are new. All the lingo, terminology, etc are explained there in some way in literally hundreds of videos. This may sound like a shameless plug for his youtube channel but I've literally spent hundreds of hours watching his stuff since 2015 and learned so much in the process. If you are new to the hobby, this is a must.
Painless 360 YouTube Channel
As for the sensing and tracking features, it would be very hard or impossible to build one that would do all those things effectively for less trouble and money the aforementioned Mavic series could. Things like object sensing and tracking are still very proprietary software options and you're not going to make this yourself currently. As stated in the previous answer: Just buy it from DJI if you really need those features. Otherwise, build your own. It's a blast. |
H: How do I re-charge the batteries of my S49 drone faster when outside?
I have a small S49 quadcopter. After around 10-15 minutes, it often runs out of charge and needs recharging. My charger requires it to be plugged into a portable USB charger or to the mains. I have tried charging using my power bank, but it takes like 30 minutes to charge compared to 10 minutes at home using the mains.
What other methods of charging could I use to charge it that will preferably charge it faster?
AI: I couldn't find manual or just the specifications for this exact drone, but from what you wrote and what I see on the images it uses 1-Cell batteries charged with some USB adapter.
You didn't specify which USB power-bank you have or which power adapter you use to charge from the mains.
I assume it's some-kind of phone charger. These days phone chargers typically outputs current of 1.0-2.0A. So my guess is that your power-bank isn't capable of outputting these kinds of current.
Try looking for a power-bank with QuickCharge (QC). They are capable of giving out currents up to 4.5A |
H: What are good specifications for a intermediate medium priced quadcopter?
What are good specifications for an intermediate medium-priced quadcopter? I have flown a smaller quadcopter before and developed a bit of an understanding of how they work and how to control it.
I would almost certainly like a camera and the drone to be First Person View (FPV) but also some more advanced features. I would like the cost to be around $200.
AI: Okay, as someone who has just recently passed through this stage, here's my take on it. Almost all of the considerations below stem from the maxim that the best drone for you is one that you will fly the most. Both progression and enjoyment in this hobby (and many other hobbies as well) are directly linked to how much time you spend doing it. Whenever you're unsure about a decision, besides other considerations ask yourself which option will keep you in the air more.
Now, to the list itself. Your "second" drone must be:
Indestructible. Durability is valuable for all quadcopters intended for acrobatic or racing flying, and you'll likely never stop bashing your drone into stuff no matter how high your skill, but unlike the pro pilots who probably break more drones a month than you will ever own, you don't have spares lying all over the place for when you do. For a long time, this is likely going to be the only "real" drone you'll own, so it better be durable. There are two main ways you can achieve that:
The "classic" approach is to have massive unbreakable arms, a titanium cage around the components, etc. That's pretty self-explanatory, though you'll have to pay for it in added weight (which is not that bad if you don't carry a gopro).
The other way is for the drone to be so light that it simply doesn't
have enough inertia to break anything, including itself or even its
own props. This is the idea behind the "toothpick" class of
quadcopters, which some consider an excellent choice for
beginner-intermediate pilots, in part for this reason.
Basic, but high-quality. What I mean by that is that you don't need the fanciest F-infinity processors, top-end performance motors, the lowest-latency camera, etc. What you do need, however, is for all the components to be high-quality and well-built by a reputable manufacturer. i.e. an F4 FC made by a well-regarded manufacturer is better than an F7 FC by a knockoff noname brand. Not only will this reduce your cost (by picking basic components) and add to reliability (by picking trusted brands), it will also make things simpler for you and less heartbreaking when you do break something.
Easy to maintain. However durable your drone, you will crash it, break something and need to fix or replace it eventually. And when it happens, you'll want your drone to be easy to disassemble and reassemble, have replaceable parts, etc. First, this rules out the non-DIY type of drones, but the DIY ones are also not created equal. Some frames make accessing the guts as easy as unscrewing three bolts, while others need more disassembly. A bigger drone is significantly easier to work on, with less tiny fiddly parts, while a small one (3" and smaller), while frustrating to work on at times, will likely break less. For larger (5 inch +) frames, replaceable arms are a very good feature to have, and a simple replace procedure (i.e. unscrewing one bolt versus disassembling the whole frame) is important as well. Toothpicks are an interesting class in that regard, in that they have a tiny whoop-like architecture, with only 4 parts: the frame, motors, camera, and an all-in-one FC+ESC+VTX board which the motors just plug into with pin connectors. This makes them way easier to maintain than other quads of this size, but also less upgradable, since three of the main components are on one board. Which brings us to...
Upgradable. This is closely related to the previous point, but slightly different. You want to be able to swap any of the major parts of the drone (FC, ESC, motors, camera, VTX, frame, etc.) for a different or better model without also having to swap the others or encountering any compatibility issues. This is mainly a jab at some prebuilt quads that have proprietary components in them which would not work well or at all with other off-the-shelf components.
Fit for your usual flying location. This is actually important for any quad, but as this one is likely to be the only one for some time, here it is especially important. The best quadcopter is one that you fly a lot, and so you want yours to be well-suited for the size, configuration, weather conditions and other considerations at the place where you fly the most, as this will maximize your flying time, frequency of flight sessions and enjoyment of the process, all very important contributing factors to how fast you learn and how much you enjoy the hobby. If you buy "the best-flying" copter but it won't fit in your flying field, you won't fly it much at all. The most important parameter here is likely the size class of your copter, which must fit the size of your location. Loosely, it's something like this:
if you mostly fly indoors, you need a tiny whoop (although it's likely you'll later want a separate outdoors quad anyway)
for a playground/backyard-sized outdoors location with lots of small obstacles (i.e. literally a children's playground) and gaps a larger (75-85) brushless whoop or ~2 inch quadcopter with detachable propguards will offer the most
enjoyment out of flying in such a tight space while still being able to rip in larger locations.
For something like an uncrowded street, large backyard or small park a toothpick-class 2.5 to 3 inch quad would be optimal;
for larger parks you can go either the toothpick or the 4-5 inch route, depending on how crowded the place is; the former is safer for everyone, less intimidating, and slightly slower, while 4-5 inch quads are noisy, heavy and can do some damage, but are still the undisputed leaders when it comes to flight performance.
finally, if you've got huge fields, shorelines or even mountains to fly over, you probably want a 5 or even 6 inch quadcopter that is able to cover the distance well. However don't fly too far without educating yourself on proper long-range operation first, there's a lot of stuff that you need to know (and buy :) in order to not lose your precious quad a couple km away in the first few flights.
Of the quadcopters that fit all the previous points, choose (or build) the one that you like the most subjectively. Maybe it looks cool, maybe you really like the manufacturer, maybe it's elegant. The factor of likability should not be underestimated. Whatever the reason for you to love the quad, the more you do, the more love, time and effort you'll put into it, making it a better quad and you a better pilot!
As a final word, I must reiterate. Whichever quad you pick, in the end the most important thing is that you fly a lot. Buy a good amount of batteries, a nice flight backpack, and make a habit out of going out and flying. You'll love every moment of it and of the rest of your life as well. |
H: How do I pick my gear when getting started with FPV multirotors?
There are a large number of beginner and starter kits out there for people looking to get into multirotor FPV flying, all touting their various advantages over the competition.
What should I look for (or avoid) in an FPV drone kit, as someone who hasn't flown FPV before?
AI: There are quite a few aspects of FPV, so a I’ll give a summary here. I’ll try to be concise so if any extra info is required or wanted, please let me know.
The first thing to look at when you’re flying FPV is the kind of aircraft, all the way up from a small Tiny Whoop to an X class (please not for beginners though!). In general, the larger props tend to give more flight time up to a point - it’s generally agreed that 7 inch props should be used for long-range because of this.
Video Transmitters
Another important thing to look at on your aircraft (excluding the advantages of different flight controllers etc, which I would love to talk about but would end up writing a massive wall of text) is the video transmitter, or VTX.
When looking at these, the first important thing is to check your local laws about what frequencies and transmitter powers you can use. Once you know that, keep in mind that more power tends to equal more range in open spaces, but can lead to more interference in places like abandoned buildings.
Another important fact to remember about the VTX is that you should manually select the channel on your VTX AND goggles as auto-scan sometimes picks the wrong channel and will cut out after a few feet. Also, never turn on your VTX without an antenna installed, or you risk damaging it. It is perfectly normal for your VTX to get warm on the bench when there is no airflow.
Finally, you will see people talking about Smart Audio - this is just a way to control the settings on the VTX from your transmitter.
Other hardware
Motors are very important. If possible, get brushless motors as they last longer and are more powerful.
When getting your first FPV quad, check out how repairable it is. It’s almost certain that at some point you will need to repair or modify it, so it’s good to know that before getting the quad.
Check what voltage your quad is designed to run at. If you have too little voltage, your quad will be underpowered, but if you have too great a voltage your quad may burst into flames (possibly a slight exaggeration to get a point across).
The ESC or Electronic Speed Controller is what tells your motor what to do, and you need one for each motor. If possible, get BLHeli_32 ESCs as they are more modern and natively support bidirectional Dshot so you can enable something called ‘RPM filtering).
When looking at flight controllers, the higher the value of X is in the naming format FX, the better. At the time of writing, F4 is the most common and F7 is becoming more popular. As I said, I won’t go into too much detail, but the higher the number, the more processes the CPU can complete per second so the more filtering and other leaguers you can have.
Goggles
There are two main types of goggles - box goggles and slimline goggles.
In general, slimline goggles are more expensive, lighter, arguably more comfortable and tend to have a narrower field of view and better quality displays. Box goggles, on the other hand, have massive screens and tend to be cheaper, however they are larger and heavier so may be less comfortable.
If possible, get goggles with a diversity receiver (or if you get Fat Sharks of Orqas, get a diversity receiver module like Rapidfire). This has two receivers and can either merge the two signals into one (cleaner) signal, or just automatically pick whichever signal is the strongest.
RC Transmitters
The most commonly used protocol at the moment is FrSky's D16, with Crossfire becoming more and more popular not only for long-range, but just for general flying.
When picking your transmitter, look for Hall gimbals, which use the Hall Effect to measure movement instead of potentiometers, so last longer and (apparently- I haven t used them) feel nicer.
Much of your transmitter will be personal preference, about the ergonomics and whether you pinch, thumb or hybrid-pinch.
Batteries
For anything more than 1S, you need a balance charger to make sure all the cells have the same voltage. To find the nominal voltage of a battery, multiply the number of cells by 3.7, as the nominal voltage of a single cell is 3.7.
I will leave you with this - don’t leave charging batteries unattended - LiPos are very dangerous if mistreated and can burst into flames if damaged or overcharged. |
H: Getting Started with Aerial Photography
There are a large number of camera drones on the market covering a vast range of cost, from hundreds to thousands of £/€/$/etc.
What are the things to look out for in a photography drone for someone looking to try amateur drone photography?
Please focus on the drone specific elements, such as camera gimbals, stabilisation, etc.
Discussion on cameras is welcome and relevant, but when going into detail consider that this is a drones question rather than Photography.
AI: When looking for camera drones, there are several things to look out for:
GPS is a big one. It allows the quad to hold its position so you can line up the shot perfectly. It also allows auto-return functions and flight tracking.
A 3 axis gimbal is also important. You can get away with 2 axis, but three is much smoother. This allows you to angle the camera properly and holds it steady so you can get the perfect shot. It is also very useful for filming as it removes the actions of pitch and roll, and reduces yaw.
Large prop are helpful as a larger wheelbase generally means more stability.
Not that it needs saying, but brushless motors are a must.
And FPV feed to a phone or other monitor is essential to line up your shots, and also relays useful information about the state of the aircraft.
For filming, you’ll want a neutral density or ND filter in bright conditions to make the footage smoother and add motion blur (not essential but can make footage look better).
Finally, you’d obviously want excellent battery life (at least 25 minutes) to give you time to set up and get the shot you want. |
H: Are there specific laws or regulations in the USA barring weapons on drones?
Are there specific laws or regulations in the USA on operating an armed drone, or do armed drones fall under ordinary weapons laws? More specifically, is it legal to fly a drone with a weapon under the following conditions:
The weapon is one that the drone pilot can carry legally in the jurisdiction in which the drone is flown (e.g. pilot is not barred from having the weapon under Federal, State, or local law; they possess a license to carry the weapon if required under local law; etc.).
The weapon is not installed on the drone for the purpose of committing a criminal offense (e.g. performing a murder or assault), but for peaceful or at least lawful reasons.
Restated, is a drone considered an extension of a person's body for purposes of determining if a weapon is lawful, or is there a specific regulatory regime for determining if an installed weapon is legal for drone carry?
To be clear, I'm not asking for specific legal advice, but inquiring whether the USA has provisions specifically regulating weapons on drones or whether drone weapons fall under ordinary (non-drone) weapons law.
AI: I’m not a legal expert, but according to the following link to an FAA page, it is illegal to attach any dangerous weapon to a drone: https://www.faa.gov/news/updates/?newsId=94424 |
H: Flying a drone in France
In the future, I plan to fly a small (<250 gram) in France, are there any special licenses/permits that have to be obtained? What are the laws on this? Where are the no-fly zones located?
AI: You mention that this will be in the future. While the other answer covers the current situation well, you should note that the rules are due to be harmonised across Europe and this might introduce some changes.
https://dronerules.eu/en/recreational/eu_regulations_updates
The following image summarises the requirements for the new regulations:
This table refers to the new classes, which are intended to make it easier for a consumer to tell what they can do with their drone (new drones should show their class on their packaging) [source]:
Class C0 - (can be flown in all subcategories) Very small unmanned aircraft, including toys, that:
are less than 250g maximum take-off mass
have a maximum speed of 19m/s (approx. 42.5 mph)
are unable to be flown more than 120m (400ft) from the controlling device
Class C1 – (can be flown in all subcategories) Unmanned aircraft that:
are either:
less than 900g maximum take-off mass, or;
are made and perform in a way that if they collide with a human head, the energy transmitted will be less than 80 Joules
have a maximum speed of 19m/s (approx. 42.5 mph)
designed and constructed so as to minimise injury to people
The standards also cover other aspects such as noise limits, height limits and requirements for remote identification and geoawareness systems.
Class C2 – (can be flown in subcategory A2 [close to people] or A3 [far from people]) Unmanned aircraft that:
are less than 4kg maximum take-off mass
designed and constructed so as to minimise injury to people
are equipped with a low-speed mode’ which limits the maximum speed to 3m/s(approx. 6.7 mph) when selected by the remote pilot
The standards also cover other aspects such as noise limits (but different from C1), height limits and requirements for remote identification and geoawareness systems, plus additional requirements if it is to be used during tethered flight.
Class C3 – (flown in subcategory A3 [far from people] only) Unmanned aircraft that possess automatic control modes (such as found in typical multicopter ‘drones’) which:
are less than 25kg maximum take-off mass
The standards also cover other aspects covering height limits and requirements for remote identification and geoawareness systems. There are also additional requirements if it is to be used during tethered flight, but there is no specified noise limit (because the aircraft is intended to be flown ‘far from people’).
Class C4 – (flown in subcategory A3 [far from people] only) Unmanned aircraft that do not possess any automation, other than for basic flight stabilisation (and so are more representative of a ‘traditional’ model aircraft) which:
Are less than 25kg maximum take-off mass |
H: One motor on quadcopter broken
I have a small quadcopter and I realised one of the motors does not turn electronically, meaning it can't fly properly. There is no visible sign of something stuck in the motor, like some string or something. What can I do to diagnose/fix the issue?
AI: So this method will vary based on whether they are brushed or brushless motors.
For brushed:
Spin the propeller with your fingers - is anything actively resisting the motion?
If yes, remove the prop and check for something not immediately visible, like a hair or carpet fibres caught around the motor shaft.
Remove anything you find and try the prop again.
If nothing is resisting motion, check the connections between the FC and the motor.
If all else fails, swap the motor with the one diagonal from it. If the problem travels, the motor is at fault. If not, there is trouble with the board.
It is worth noting that brushed motors are a consumable - the brushes wear out, and most aren’t rated for more than a number of hours’ use - see the diagram below:
(Image Source)
If the motor is brushless, start by again turning the motor, and check no screws are touching the windings.
Check all motor connections and see if there are any breaks.
If there is not active resistance, swap over two of the motors. If the problem follows the motor, it is likely a problem with the motor. If not, there is a problem with one of the ESCs.
If you do encounter active resistance, look inside the bell and see if any of the magnets have slipped. If they have, use epoxy and tweezers (though a toothpick also works well) to glue the magnet back in place. I’d recommend also buying a new motor as it is now likely to be slightly unbalanced which may cause oscillations.
See diagram of brushless motor:
(Image Source) |
H: How to tell if you have a brushed or brushless motor?
I understand there are 2 main types of motors: brushed and brushless motors. How can you tell visibly what type of motor you have without researching/reading the manual?
AI: As a general rule-of-thumb, brushed motors usually have two wires, while brushless motors generally have three.
Image source |
H: Differences between brushed and brushless motors - advantanges and disadvantages of each
When buying a drone I have 2 options to consider: brushed and brushless motors. Are they much different from each other? Does one have advantages over the other?
AI: They are very different.
Brushed motors
Brushed motors are good for toy grade drones for a couple of reasons: they are cheaper and don’t require ESCs, which would add extra cost and complexity.
Brushless motors
However, in almost every way brushless motors are better: they produce much more power, are more efficient, produce more torque and, my favourite part, they don’t have physical brushes and so, unlike cheaper brushes motors which are only designed to run for a number of hours, brushless motors can take a lot of abuse and can last for years. Additionally, they are very water-resistant.
There are downsides: to a brushless motor - they require ESCs and, due to the torque, can do more damage in a crash.
For info on how each works, see my answer here: https://drones.stackexchange.com/a/87/50 |
H: Optical sensors vs Ultrasonic sensors on a drone
Are there any performance differences between optical sensors and ultrasonic sensors? How do I make the right choice for my drone? I will be using them in a object detection system for collision prevention.
AI: Keyence has a useful comparison table:
╔════════════════════╦══════════════════╦══════════════════╗
║ Item ║ Optical ║ Ultrasonic ║
╠════════════════════╬══════════════════╬══════════════════╣
║ Detectable target ║ Affected by ║ Unaffected by ║
║ ║ colour/material ║ colour/material ║
║ Detecting distance ║ 1000mm max ║ 10m max ║
║ Accuracy ║ High ║ Low ║
║ Response speed ║ Fast ║ Slow ║
║ Dust/water ║ Affected ║ Unaffected ║
║ Measuring range ║ Small ║ Large ║
╚════════════════════╩══════════════════╩══════════════════╝
So basically it depends how and where you want to use it... Since you say you are trying to avoid colliding with objects, my guess is you'll want the ultrasonic. It gives you a much higher detecting distance (10 m vs 1m). At most speeds, 1 m could be insufficient to avoid a collision.
Also, if you plan on using your drone anywhere where the sensor could get dirty/wet, you'll definitely want to go with the ultrasonic sensor. |
H: Barometer vs Rangefinder
On a small 6-7inch drone do I need a barometer, rangefinder or both? Is there a standard practice or does it just depend on use case?
AI: Technically, you don't need a rangefinder or a barometer for a normal drone but if you want to make a drone with altitude hold, I would recommend a barometer over a rangefinder because a rangefinder will not work very high up or when you are flying over certain surfaces like water. A rangefinder would only be good if you stay close to the ground and don't fly over reflective surfaces. |
H: Effect of motor load on ESC?
I know that when a prop is caught on something or is slowed down by something it can put extra strain on the ESC or even burn it out.
If I was using a 2207 motor with an unusually large and heavy prop, would I need a more powerful ESC to compensate for the extra load of the large prop?
Would the ESC just need a higher Amp rating in order to operate under the increased load?
AI: The primary thing that high torques affect in a brushless motor is the current flowing through. It obviously affects your ESCs, but also the motors themselves: high currents have been known to melt/burn the insulation on motor windings, which then short out and wreck the motor itself and possibly the ESC as well.
If the source of this torque is just a prop, the best way to see the actual effects of it on your particular motor would be to find a datasheet/spec sheet for it that lists thrust and current consumption for different combinations of supply voltage, prop, and throttle percentage, like this one:
Not all manufacturers provide this kind of data, however. If yours doesn't, or you desire additional information, it's a good idea to browse the site miniquadtestbench.com. They publish the same kind of data, gained from thrust-testing a big range of motor-prop combinations in the lab, and have a handy search tool to find and compare test results for different motors, props and throttle settings. The graphs might be somewhat confusing at first, though:
MQTB tends to use a greater variety of actual props, but the selection of motors is understandably limited.
If you don't find data on your particular motor in either of these sources, and you only need a ballpark, looking at specs of other motors of the same size and KV should be reasonably close, likely to well within ±10%. |
H: Difference between analog and digital servos?
I've noticed that there is often a price gap between analog and digital servos. What is the difference between an analog and digital servo and why is a digital servo better?
AI: Analog Servos
Analog RC servos use a form of pulse width modulation (PWM) to control the speed of the servo. It's basically switch the motor on and off quickly (Commonly 50 times per second). The motor rotates a certain angle depending on the width of the on-pulse.
Digital servos
Digital servos also use PWM, but at a much higher frequency (6 times that of a analog servo). They contain a microprocessor that received the signal, and then send the PWM to the motor
Comparison
The digital motor will be smooth and react faster, but it's more complex and therefore more expensive |
H: Headless mode on a drone
I have noticed my drone has headless mode listed as one of it's features.
This poses a few questions:
What does this mode do?
How is it different from normal mode?
How does it work?
How do I enable it?
AI: What is headless mode?
Headless mode is a specialized flying mode that is common in store-bought drones. It eliminates the need for focusing on the drone’s orientation and enables a much easier Line of Sight flying experience. This can make drone flying easier especially for beginners still learning how to control the flight path of the drone.
Whilst it may be useful for beginners to learn flying using this mode, it wouldn’t be too recommended. You can then get used to this mode and then have trouble unlearning it and learning how to fly the drone properly.
The only thing is that when you launch the drone, the front of the drone must be facing away from you to launch properly.
How does it work and how is it different to normal mode?
When you take off with the drone pointing forward, algorithms within the drone’s microcontroller will ensure that any directional changes are compensated. The drone will take instructions based on your current orientation as opposed to normal mode where the drone moves in regards to the drone's orientation, no matter where you are regarding the drone.
For example, if you are in normal mode and the drone is facing toward you, and you press left, the drone will go right (as left in the way it’s facing means right in the way you are facing) whereas, if you are in headless mode, the drone will move left in the direction you are facing the drone.
This diagram illustrates how normal mode is different from headless mode:
(image source)
This is another diagram showing a more detailed visual of how the drone will move differently in normal mode compared to headless mode:
(image source)
How do I enable it?
This will vary from drone-to-drone so one specific answer cannot be given. If your drone has it built-in (which most do), there should be something in the instruction manual saying how to enable it. Most likely it’s a button that needs to be pressed on your controller. |
H: Keep quadcopter steady when taking a video
Whenever I take a video on my small quadcopter, it’s never steady. It always bounces up and down a bit rather than keeping level. How can this be stopped/prevented?
AI: I'm going to assume that you don't need your videos to be stabilised realtime. In this case you need image stabilisation software.
I'm not an expert in this field particularly, so I'll copy the most relevant answers on this reddit thread.
If it's a smoothing stabilisation like this, you can use VirtualDub
and Deshaker (Tutorial), Ffmpeg (Tutorial) which are all free or you
can use After Effects - Tutorial. There's also a Stabilization bot
called stabbot which will do it for free. Check out r/stabbot. It uses
Ffmpeg/vid.stab. |
H: In drone racing with multirotors, how does one navigate the course?
Whenever we watch drone racing, there is usually a course marked out in cones.
However, when there is an obstacle such as a Jacob’s Ladder, the racers know the order to go through each of the gaps. Similarly, we sometimes see racers fly through the same gate twice in a row.
How do they know to do this?
Is there a special way of marking out the course that is universal, is there a briefing prior to the race, or is there another method?
AI: I've gone out and asked an actual racer about this one.
There are usually some visual cues. The course is laid out in cones, the flags are asymmetrical so you know on which side you should pass, the gates you must fly twice through usually have something (bright fabric, a flag, ...) next to them on the side that you fly around before going back into the gate, etc. and the cones themselves are not just a flat string but are laid out in certain patterns; for example, when the sequence of cones terminates in an arrow this usually indicates you should go upwards (or higher, i.e. in the case of two gates stacked on top of each other), while a perpendicular line marks the entry point of the cone string.
Sometimes the track elements are colored differently (and asymmetrically) to indicate the direction. Some elements just have canonical uses based on their shape: you should pass through gates, fly besides flags, dive the dive gates... The Jacob's ladder specifically is almost always passed top to bottom in sequence (while whether you should go right or left varies track to track).
That said, there is no universally accepted, set-in-stone standard for these cues. Which ones are used depends a lot on the materials available to the race organizers, how much time they have to set up the track, the track's layout, etc. For instance, flags can either be fabric on a springy pole (in which case you fly on the convex side), or they can be inflatable and curved to hang over the ground (in which case you fly under the overhang on the concave side).
Most drone racing leagues have their own standard of how different track elements and maneuvers should be marked on the racetrack and try to stick to it. Even then some smaller local or regional events of the league may be limited by the organizers not having all the required materials. Also, one cannot mark everything on the more complicated, technical tracks, or mark it in an unambiguous manner. Sometimes some parts of the track are formed by the terrain itself, i.e. an abandoned building or natural rock formation. In that case there's no standard and the track designers must get creative to even make it clear where the gates are!
So visual cues aren't everything. A lot of races rely on communicating to pilots how the track should be flown before the race. Sometimes it's a verbal briefing, sometimes a printed schematic. Sometimes the track is published well in advance so pilots could train on their home field or in a simulator. There could even be a video walkthrough or a DVR of a practice run. Additionally, many leagues actually perform a physical walk through of the track on or before race day (much like Formula 1 car racing), so that the marshals and pilots can discuss challenges, specific items and hazards, etc.
In the end, for serious racing, how the track itself is marked does not matter. During the actual race the speed at which everything is happening does not leave you any time to think or figure out what's coming next by parsing the track. The racer just knows in advance which gate or maneuver comes after the one he's flying through, and anticipates it, most likely along with the one after that as well. Knowing the track is a very important factor in winning a race, as in order to have the fastest (which usually means shortest) trajectory, the pilot must start the necessary maneuvers for passing the next gate while he has not yet passed the previous one.
Besides training beforehand and learning the track from the given materials, the racers are always allowed to fly some laps around the actual final track before the race in order to memorize its layout. This is critical as the actual racetrack will always slightly differ from whatever training track they might have constructed for themselves. During these training laps they also figure out the best way to tackle the elements of that particular track in the speediest way possible, and thus develop an optimal trajectory, or racing line, as it's usually called.
So, in the end, the on-track markings are there just to aid in the initial few laps as the track is being learned by the pilot, and after that, memory takes over. |
H: Beeper beeps if transmitter is turned of even if it shouldn't
I have turned off all beeper sound signals in Betaflight Configurator, but the beeper still beeps if the transmitter is turned off. I thought that that shouldn't happen when RX_LOST was turned off or not paired, but maybe I have understood it wrong? Or is a bug or a problem with my setup in some way?
Here is my diff all:
#
# diff all
# version
# Betaflight / STM32F405 (S405) 4.1.5 Mar 16 2020 / 05:19:58 (d4e74e39c) MSP API: 1.42
# manufacturer_id: AIRB board_name: OMNIBUSF4SD custom defaults: YES
# start the command batch
batch start
# reset configuration to default settings
defaults nosave
board_name OMNIBUSF4SD
manufacturer_id AIRB
mcu_id 003c00403436511339373635
signature
# resources
resource SERIAL_TX 1 NONE
resource SERIAL_TX 11 A09
# feature
feature SOFTSERIAL
feature TELEMETRY
# beeper
beeper -GYRO_CALIBRATED
beeper -RX_LOST
beeper -RX_LOST_LANDING
beeper -DISARMING
beeper -ARMING
beeper -ARMING_GPS_FIX
beeper -BAT_CRIT_LOW
beeper -BAT_LOW
beeper -GPS_STATUS
beeper -ACC_CALIBRATION
beeper -ACC_CALIBRATION_FAIL
beeper -READY_BEEP
beeper -DISARM_REPEAT
beeper -ARMED
beeper -SYSTEM_INIT
beeper -ON_USB
beeper -BLACKBOX_ERASE
beeper -CRASH_FLIP
beeper -CAM_CONNECTION_OPEN
beeper -CAM_CONNECTION_CLOSE
beeper -RC_SMOOTHING_INIT_FAIL
# map
map TAER1234
# serial
serial 0 64 115200 57600 0 115200
serial 2 2048 115200 57600 0 115200
serial 5 16384 115200 57600 0 115200
serial 30 32 115200 57600 0 115200
# aux
aux 0 0 0 1700 2100 0 0
aux 1 1 3 1300 1700 0 0
aux 2 13 2 1300 1700 0 0
aux 3 35 2 1700 2100 0 0
aux 4 36 1 1700 2100 0 0
aux 5 39 3 900 1300 0 0
# rxrange
rxrange 0 987 2011
rxrange 1 987 2011
rxrange 2 987 2011
rxrange 3 987 2011
# vtxtable
vtxtable bands 6
vtxtable channels 8
vtxtable band 1 BOSCAM_A A FACTORY 5865 5845 5825 5805 5785 5765 5745 0
vtxtable band 2 BOSCAM_B B FACTORY 5733 5752 5771 5790 5809 5828 5847 5866
vtxtable band 3 UNKNOWN U FACTORY 0 0 0 0 0 0 0 0
vtxtable band 4 FATSHARK F FACTORY 5740 5760 5780 5800 5820 5840 5860 0
vtxtable band 5 RACEBAND R FACTORY 0 0 5732 5769 5806 5843 0 0
vtxtable band 6 IMD6 I CUSTOM 5732 5765 5828 5840 5866 5740 0 0
vtxtable powerlevels 2
vtxtable powervalues 0 1
vtxtable powerlabels 25 200
# master
set gyro_sync_denom = 2
set dyn_notch_range = LOW
set dyn_notch_width_percent = 0
set dyn_notch_q = 200
set dyn_notch_min_hz = 90
set acc_trim_pitch = 4
set acc_trim_roll = -6
set acc_calibration = 40,-16,-19
set min_check = 1010
set max_check = 1990
set rssi_channel = 9
set serialrx_provider = SBUS
set dshot_bidir = ON
set motor_pwm_protocol = DSHOT300
set vbat_scale = 108
set small_angle = 180
set pid_process_denom = 1
set osd_rssi_pos = 2426
set osd_rssi_dbm_pos = 120
set osd_tim_2_pos = 2455
set osd_flymode_pos = 2401
set osd_current_pos = 2440
set osd_mah_drawn_pos = 2448
set osd_warnings_pos = 14602
set osd_avg_cell_voltage_pos = 2433
set osd_flip_arrow_pos = 2095
set osd_stat_max_spd = OFF
set osd_stat_battery = ON
set vtx_band = 1
set vtx_channel = 1
set vtx_power = 2
set vtx_freq = 5865
set vcd_video_system = NTSC
set gyro_1_align_yaw = 2700
set gyro_rpm_notch_harmonics = 1
profile 0
profile 1
profile 2
# restore original profile selection
profile 0
rateprofile 0
# rateprofile 0
set roll_rc_rate = 90
set pitch_rc_rate = 90
set yaw_rc_rate = 90
set roll_expo = 35
set pitch_expo = 35
set yaw_expo = 35
set roll_srate = 80
set pitch_srate = 80
set yaw_srate = 80
rateprofile 1
rateprofile 2
rateprofile 3
rateprofile 4
rateprofile 5
# restore original rateprofile selection
rateprofile 0
# save configuration
save
#
AI: I found the problem: RX_LOST was disabled, but RX_AUX wasn't. I have the beeper set to beep if i center a swich, and since that is the default in Betaflight, the beeper turn on because it thought the switch was in that position.
I opened an issue about it here:
https://github.com/betaflight/betaflight/issues/9717 |
H: When flying FPV in a group, what are the best video transmission channels/frequencies to use to avoid interference?
When flying FPV drones in a group setting it is very important to choose appropriate video transmission frequencies so you don't interfere with others that are flying near you. What are the best channels to use ( depending on where in the world you are ) for groups of 2-6 people?
AI: To answer this question, there are two things you need to know. First you need to be able to map the various channels and bands to their frequencies. Second, you need to understand Intermodulation Distortion (IMD). The quick explination of IMD is that two or more radio frequencies can combine to cause interference on a third frequency.
Using the above chart you can see how the different bands and channels overlap. In general, when flying with just one other person, you are fine to choose any two channels that don't overlap frequencies. However as you add more people to the mix, you have a higher chance of causing IMD. To help with that issue, many races now operate using a group of channels called IMD5 or IMD6.
If you are in a group of 5 people, the recommendation is to use R1, R2, F2, F4, and E5. If you are in a group of 6 people, use R1, R2, F2, F4, F8, and R8. |
H: What affects the total flight time for a drone?
What factors would affect a drone's flight time? Battery capacity? Weight? Anything else?
AI: I'd watch out for several factors:
1. Weight
Drop any additional weight that you don't absolutely need for functioning. This may mean downsizing to smaller motors, which obviously means that you have to balance weight vs. power; you may be able to get your flight time much longer but at the expense of speed.
2. Battery
Obviously the more juice you got, the longer you can go for. Again, though it's going to be a balance between the weight of your battery... go for lighter technologies like LiPo.
Also, make sure you've got new batteries on your drone; as your batteries age, they'll lose juice and capacity.
3. Motors
If you really want to increase the flight time... go for lighter less powerful motors. Of course, you won't be able to go as far, so that may not be a tradeoff you want to make.
4. Weather
Make sure you're flying your drone in dry weather... Condensation or water droplets will both add resistance to any moving parts and weight. Also, when the weather is well below freezing you'll notice that your batteries will start performing less well, as well as having increased friction.
5. Maintenance
Keep all moving parts well greased! As friction increases, the amount of battery power you use will increase in consequence.
Also, make sure all contacts remain solid. Though it's not a big issue with newer drones, rust in the contacts / loose contacts will eat power. |
H: How fragile are the SMA connectors used in FPV equipment?
I've heard that it is a terrible idea to install and remove SMA antennae from my goggles every time I need to pack it away after a flight session. I know that this is because the SMA connector is fragile and wasn't designed for a high mating cycle rating, but how serious is the concern that the SMA connectors on my googles will break?
If I began taking off my antennae when I need to pack it away, how quickly would the connectors break or terribly attenuate the signal?
AI: According to electronics-notes.com, the mating cycle rating for the SMA/RP-SMA connector is 500 cycles. However, it is important to note that this rating assumes that the connection and disconnection process happens as smoothly as possible, with the body of the connector not moving at all while the screw connection is tightened sufficiently to not allow the joint to shift while connected. Under nonideal conditions, the actual lifespan of the SMA connectors on FPV goggles is likely to be far shorter.
Under the best of circumstances, the connection would likely last: (assuming one mating cycle per flight session)
~19 years @ 2 sessions/month
~9.5 years @ 1 session/week
~5 years @ 2 sessions/week
~2.5 years @ 4 sessions/week
~1.4 years @ 7 sessions/week
From this, we can see that the answer likely depends on how often you fly and how long you would like your goggles to last. Although the attenuation (signal strength reduction) of the connector will increase with every mating cycle, if you fly infrequently enough it is possible that you may be ready to upgrade to a new goggle by the time that the SMA connectors begin to become a serious problem.
If you take care to make and break connections cleanly, casual pilots who don't fly very often might not see too much of a problem, but more serious pilots who fly more than once a week definitely shouldn't be removing their antennae on a regular basis. |
H: Can I configure Betaflight in the field without using a laptop?
I often find myself wanting to make adjustments to the settings on my quadcopter in the field, especially when tuning PID settings and rate profiles. I currently bring a laptop with me wherever I go so I can plug in over USB and use the Betaflight configurator, but it's very annoying to keep with me when I go fly.
Is there any way I can edit the settings on my Betaflight quad in the field without using a laptop?
AI: Yes, you actually can! There are a couple of options for the Betaflight firmware which are mostly plug and play.
OpenTX Lua Scripts
Radios running OpenTX can use scripts written in Lua to control these parameters with the radio's scroll wheel and buttons. Please see @PaulKendall's answer for an explanation of how this method works.
Betaflight OSD
If you have an FPV setup on your quad, you can make use of the Betaflight OSD to tweak the vast majority of settings you would need access to during a flight session, like the PID values and rate profiles you mentioned. The OSD makes use of the sticks on your transmitter to navigate the menus, which appear as an overlay on top of the camera feed from the quad.
As described in this article by Oscar Liang, the stick combination mid throttle, yaw left, pitch forward, roll centered is used to enter the menu, which should look something like this:
From here, pitch up/down is used to navigate up and down in the current menu, and roll right to select an option or enter a sub-menu. (items with arrows on the right side are sub-menus) The roll axis is used to change a value up/down.
I know this sounds confusing, but it makes a lot more sense once you try it out and gain experience working with it. Remember to select the SAVE REBOOT after making a change and before going back to flying, or your change likely won't take effect!
Speedy Bee Smartphone App
If you want an experience that is closest to using the desktop Betaflight configurator or don't have an FPV setup on your quad to use, the Speedy Bee smartphone app for iOS and Android may be a good option. You can connect to the quad either using Bluetooth (you must have a Bluetooth module already installed on your quad), or over USB (USB OTG mode is only supported on Android).
Because this app is developed and maintained by a third-party and not the Betaflight project, some new settings aren't likely to be accessible with this app, but it should work for most common settings. I suggest watching Joshua Bardwell's video about this app for more details. |
H: How hot is too hot when it comes to multirotor motors?
I hear this question asked all the time. Are my motors getting too hot? How hot is too hot for motors to get? Anyone have a great way to answer this question, possibly with some temperatures?
I generally go by feel. If I can pinch the motors with my fingers for at least a few seconds without feeling like they will burn me, I know the motors are not too hot. I know a lot of people would like a more scientific answer than that.
AI: Temperature is a killer of motors over time. If motors are exposed to prolonged heat, the magnets in the rotor lose their magnetic field strength over time and consequently reduce the lifespan of the motor.
Generally, a well-tuned drone should not have extremely hot motors after flying (with a few exceptions). It depends on the motor, but you should avoid raising the motor’s temperature past 170°F; any hotter, and you run the risk of damaging the rotor’s magnets and decreasing performance and longevity.
https://dronenodes.com/drone-motors-brushless-guide/
https://www.rcgroups.com/forums/showthread.php?1329288-Normal-brushless-motor-temperature-range |
H: How to create a motor startup tone with a BLHeli ESC?
I am using a 32bit DShot1200 ESC, how can I make a custom startup sound for when the drone is powered on?
AI: First, remove your props, plug your quad into the computer and plug in a battery.
You then need to go into BLHeli Suite 32 and read your ESC setup.
You will then have options to sync ESC music and you can upload your tones.
A more detailed guide with lots of detail for each step can be found here: https://oscarliang.com/blheli-32-custom-startup-tone-music/ |
H: Series or parallel connection for drone batteries?
What is the difference between adding two drone batteries in series vs a parallel connection for flying the drone?
AI: Batteries in series = add the voltages, ie two 3S 1300 30C packs becomes 6s 1300 30C.
Batteries in parallel = add the capacities, as above you get 3S 2600 60C.
There's no particular pros or cons for either, many larger commercial drones use combinations of packs in series and parallel to get the power source they need.
For smaller quads though the overhead you get in extra weight from the leads, connectors and wiring is greater so it's generally less practical. |
H: How do you waterproof your electronics?
I fly FPV drones a lot in the winter where it is wet and snowy. What is the best way to protect your equipment from shorting out from water?
AI: The first step I take to help protect my gear from shorting out from water is to apply silicone conformal coating to all the electronics I can. I cover the ESC, flight controller, vtx, and any other exposed electronics. I find that this also provides some protection from random solder drips or conductive grains of sand.
However you have to be very careful because conformal coating will block electrical signals that you want to work, like your USB port. Also don't coat the barometer if you FC has one.
What other tips do people have for protecting their gear from bad weather? |
H: How to use an XM+ receiver without a flight controller?
All of the model aircraft I have seen without flight controllers normally have a receiver with all of the channels separate. Is there any way I can use a receiver like an XM+ receiver on a model aircraft without a flight controller?
AI: Yes, you most certainly can. The device you will need is called an SBus Decoder, which splits the SBus serial signal from your FrSky XM+ into several different PWM channels.
Example of an 8-channel SBus decoder
Example of a 16-channel SBus decoder |
H: What is a filtered power pad on flight controller?
Having looked at many different flight controllers I saw that many of them have filtered power pads. What does it mean when it says filtered power?
AI: Without knowing more specifics about the board(s) you're asking about, it's more than likely that the filtered power pads on your flight controllers are just the normal output from the 5v voltage regulator on the board which has a capacitor between the voltage regulator output and ground.
Because the 5v regulator's output is shared by all kinds of devices connected to the board, all of which consume different amounts of power and at different times, it's entirely likely that the actual voltage on the regulator's output will have some "ripple" where the voltage oscillates around 5v.
(cit.)
Some components on the drone which deal with analog signals, like the camera and VTX, may introduce visual artifacts into the image or intermittently drop out if they are fed power with too much ripple. The aim of the filtered voltage output is to smooth out the ripple so the voltage oscillations are far less pronounced. In the above graph, the solid black line is the filtered output. |
H: What's the difference between F4 or F7 flight controllers?
What is the difference between the STM32F411 and the STM32F722RET6 processors in flight controllers? What are the advantages of having the F7 processor over the F4 processor?
AI: There are a few differences:
Firstly, the F7 chip used in F7 flight controllers operates at a much higher frequency, so can handle more operations per second.
This is useful when you want to start adding lots of dynamic filters, for example RPM filtering, alongside features such as antigravity.
Whilst an F4 can handle almost anything you will want to throw at it in this respect, it will not be able to do so forever (the F3 used to be standard but is now lacking features). Therefore, F7 is better for future proofing.
F7 flight controllers also have extra UARTs. This can be very useful if you want lots of extra features, for example SmartPort telemetry, Smart Audio, GPS and camera control. However, it is not the end of the world if you don’t have as many UARTs as you want as you can use softserial to add software UARTs to your FC. Of course, this also takes up processing power so an F7 may cope better.
Finally, F7 flight controllers have built in inverters on their UART ports, while F4's do not. So an F7 FC can handle any inverted signal "as is" on any of its numerous UARTs, while F4 flight controllers have a dedicated external inverter chip on the PCB connected to one of the UARTs.
Because of that, F7's make it easier to use UARTs for SBUS or other inverted signals as it means you can hook them up anywhere without any inversion mods, while on an F4 controller you can only use the special inverted pads (of which there is usually only one, labeled "SBUS"). |
H: How to enter DFU mode on my flight controller?
How can I enter DFU mode on flight controllers, in particular on my CL Racing F4S flight controller?
Ref.: https://cl-racing.myshopify.com/products/clracing-f4s
AI: There are three ways you should know to enter DFU mode.
The first, as mentioned before, is to push down the bootloader button and power on your board.
The second method is to be used on boards that don’t have a bootloader button (which is increasingly rare). You will need to bridge two bootloader pads on your flight controller to enter DFU mode. Check the specific diagram for your flight controller to find out exactly what pads you need to bridge.
The last method is to enter the CLI and type either ‘DFU’ or ‘BL’, which will then put the FC into DFU mode. Obviously this method won’t work if you’re entering DFU mode because you ant connect to your computer. |
H: How does one hold the motor bell still when tightening prop nuts?
Almost all of the brushless motors used in hobby-grade multirotors have a single threaded shaft and rely only on friction between the propeller and motor to keep the prop from slipping. This means that the nuts holding the propeller down must be tightened with considerable force.
When I try to do this, however, while I have a good grip on the nut (via a wrench), I can't hold on to the motor itself very well to keep it from spinning together with the nut, and if I try to hold on to the propeller, it cuts me with its sharp edges. What are the available tools and/or techniques that can aid in keeping the motor still while tightening or undoing the prop nut?
AI: You know those rubber wristbands that are given out at lots of events?
You can wrap one of those around the motor bell to get better purchase on it, and then torque down the prop nut.
There are also specialised tools to hold motor bells, such as the one pictured below which can be found here, on Thingiverse. |
H: How do I tell when to replace the motors on my tinywhoop?
I own a brushed micro quadcopter, more commonly known as a tiny whoop. I've read that brushed motors in general, and especially those used in such quadcopters, have a limited lifetime and that you should replace them when they near the end of that lifetime.
However, as far as I can tell, there are no obvious signs that the motors have become too old to fly, as they don't break but instead their performance decreases over time. There's a maximum total runtime in hours listed for the motors, but I can't imagine any way to track how many hours the current set has been flown for besides writing down the length of each flight, which would be extremely tedious.
So how do I figure out whether my motors are worn out and should be replaced, or are still okay to fly with?
AI: As someone who loves collecting data for analysis, I do track all of my flights. I have found that, under normal conditions, brushed motors should last for at least a few hundred flights. You can get higher if you don't fly hard or get things caught in the props or motor shaft that will make the motor heat up more than normal.
How to determine whether a brushed motor needs to be replaced is a tough question and it really depends on your willingness to fly with a drone that isn't operating perfectly. With mine, the telltale indicator is that I notice less power than usual and yaw is off a bit (twitchy or lethargic). This makes sense since all motors perform to the level of the least capable motor. If you experience less performance, first, ensure that it's not just the battery. This is easy to do - just use a newer battery, or one that you know is still providing good power. The next thing to do, if the battery checks out, is to replace the motors. I recommend replacing all of the motors at once for brushed motors since they are all getting some form of wear while in use. Replacing them all ensures that you are starting with peak performance. |
H: Can I run two motors off of one ESC?
Normally, a dual-motor plane has two ESCs but could I connect two brushless motors to one ESC? What would happen to the torque and speed of each of the two motors connected to the ESC?
AI: Technically, you could connect 2 motors, and it will probably work if they're exactly the same size and model, and have identical props on them. However, if the motor-prop combinations are sufficiently different, most likely the system will behave quite erratically, and even if you do match the motors, there is still a good possibility of weird stuff happening anyway. To see why, though, we must dive into how brushless motors actually function.
The problem with connecting more than one motor to a single ESC stems from how these motors are driven. An electric motor works by using electromagnetic coils to pull permanent magnets and create a force on the rotor. However if you just supply current to a coil and leave it as is, at first a close-by magnet will get attracted to the coil, rotating the motor bell, but then it will just sit there in the nearest position (towards which it is being pulled), perhaps briefly oscillating back and forth like a pendulum before settling.
To create a continuous rotation, you need to stop the current as the magnet passes by and then reverse it to now repel the magnet, adding more rotational momentum to the system. In a brushed motor this switching is done mechanically using contacts (called brushes in this case) inside of the motor. A brushless motor, on the other hand, does not have this kind of mechanical switching mechanism inside, so the switching must be done externally, and this is the brushless ESC's job.
To determine when to switch the currents around, the ESC must detect when the magnets are passing the coils. To do that it constantly measures the voltages on its three terminals (as a magnet passes by an electromagnetic coil, it creates a voltage in it), and uses that information to switch the currents in the motor in perfect sync with the motor's rotation, speeding up the current pulses as the motor speeds up and slowing them down as it slows down.
Real-world ESCs and motors are not perfect, though. sometimes the ESC is incorrect in its assumptions about what the motor is doing right now or how it's going to react, and sends current pulses that don't correspond to the motor's actual position. This is called desynchronization, or, colloquially, desync, and results in the motor suddenly losing almost all of its power for a short amount of time (usually less than a second) while the ESC tries to determine the correct state of the motor and reapply power in sync with its rotation. With quadcopters this condition is most common when the motors are spinning at very low RPM, loaded by a reverse airflow (e.g. falling out of the sky bottom-down) and need to suddenly speed up, all of which mess with the ESC's expectations, and the desync can lead to a violent uncontrolled spin due to one of the motors losing power while the others successfully apply full thrust.
Now, if you connect two motors, the ESC will still think it's one motor. If these two motors are sufficiently different, the most likely thing is that one (or both) of them won't work. Different motors will both create voltages of different magnitudes when rotated, and react with different speed to currents flowing through their coils, so one of the motors will invariably get far ahead of the other in response to a current pulse, making synchronization of the two near-impossible, and leaving the ESC very confused. Depending on the ESC and motor combination, it can either give up entirely, or try to drive this weird "motor" anyway, likely leading to one of the motors spinning at reduced efficiency and the other just jerking but not spinning. If you keep this up long enough, the non-spinning one may (or may not) burn its coil windings, as these motors are not designed to sit still while high currents are passed through them.
If the motors are identical, though, e.g. of the same brand and model, and with identical propellers, they are likely to want to rotate at about the same speed and have very similar inertia, in which case they will produce more or less the same induced voltages in their wires and react the same to what's supplied by the ESC. So this setup will probably work, at least on the ground: The two motors will spin, and do that in perfect sync with each other; you can leave them spinning for half an hour and never see one propeller get even ten degrees ahead of another. Even then, nothing is perfectly matched. One motor will likely be a tiny bit ahead of the other all the time, or otherwise slightly off, which is probably not enough for triggering a desync, but means a more confused ESC and less efficiency overall, since one of the motors (or both) is going to be driven suboptimally, consuming a bit more power and producing a bit less thrust.
Further, when you mount the motors on an actual airplane, conditions may become even more unequal. Suppose that one of these "identical" propellers is chipped, or the plane is flying in a crosswind, or even that it's just in a banked turn, so one wing moves through the air slightly faster than the other. Then the load on the motors can differ considerably even though they are the same. Because of that differing load, one of them might get just enough ahead of the other to confuse the ESC into either giving up entirely, or making erratic assumptions about this weird combined "motor", leading to wrong signals being sent, which might, for example, slow down one motor and speed up the other, possibly ending in one of them desyncing and stopping entirely. This, in turn, can potentially lead to very unpredictable behavior of the model in flight.
So, to conclude this long-winded explanation, the answer to your question is:
Don't. Just don't. |
H: Difference between a 3 and 6 axis gyro
When shopping for drones, I see a 3 and 6 axis gyro available, what is the difference between the two? Does one have a advantage when flying over another?
AI: There is actually no such thing as a 6-axis gyro; the correct term for this is "IMU", which stands for "Inertial Measurement Unit". An IMU is a device that combines several inertial sensors that measure the craft's orientation and position in space.
The 6-axis IMU is a composite sensor, which contains two different types of 3-axis sensors on one chip. Usually it is a 3-axis gyroscope (which measures the rate of rotation of whatever it's strapped onto) and a 3-axis accelerometer (which measures its linear acceleration). A 3-axis gyro, on the other hand, is just the gyro and nothing else, as a standalone chip. There are also standalone 3-axis accelerometers¹, but accelerometers are almost never used in flying vehicles alone, without gyroscopes.
The third type of sensor that an IMU can contain is a magnetometer, which measures the earth's magnetic field² and can be used to tell which way is north. A magnetometer can either be present as part of a 9-axis IMU, of another sensor (e.g. in a GPS unit) or an entirely standalone unit.
Do you need the accelerometer and magnetometer? Well, it depends.
For rate mode (or acro mode, as it's more commonly known), the aircraft only needs to know its rates of rotation along all three axes and matches them to the desired rates set by the pilot via stick positions. For this, just the gyro is sufficient.
However, in attitude, angle or autolevel mode (also sometimes called stabilized mode), in which the pilot defines the desired attitude(orientation) relative to the horizon, which the drone will match, a gyroscope alone is insufficient. The flight controller will need to know not only how fast it is currently spinning, but also which way "down" is relative to itself. Due to a phenomenon called integration drift³, the flight controller can't maintain this knowledge precisely enough with just a gyro. It needs an accelerometer on board to correct the gyroscope, so if you want to use these modes, you need both a gyroscope and an accelerometer.
A magnetometer (sometimes referred to as a compass) is required for navigation modes, where besides its attitude relative to the horizon the craft has to also know its heading relative to the geographical north. Note that since navigation modes also require GPS, you could forgo the builtin magnetometer in the flight controller, and get a GPS unit with a magnetometer in it instead. Or you can get both, one in the FC and one in the GPS, which will increase the accuracy of the readings. (actually, you can double the other two sensors for the same effect; some flight controllers are manufactured with a twin IMU for that purpose.)
¹: There are also single- and dual-axis versions of each type of sensor — which only means you'll need several of those to make up a complete IMU. They are rarely used nowadays, as the integrated versions are usually better in every way.
²: Or any other magnetic field, for that matter, which is why you need to keep it away from magnets and steel structures, otherwise you'll get rubbish. There's usually little metal in the air other than what's on your aircraft, though, so magnetometers tend to work quite well in UAVs unless you've got a magnet-latched canopy and put the FC next to it or something. Minimizing interference is also why magnetometers are usually integrated into GPS units and mounted as far away from the rest of the aircraft as possible.
³: Integration drift is an issue that plagues inertial navigation since the beginning of time, and is present everywhere where you can't measure something directly, but you can measure how fast it's changing instead (in other words, you can measure the derivative of that thing). So you integrate it (add up the changes over time) to get the original value. However, every measurement comes with an error, and the errors add up as well, so your total error will grow all the time and at some point it will get bigger than the original thing you were measuring.
Intuitively, integration drift is like walking in a forest. When you enter the forest, you (hopefully) have a sense of which way north (or some other reference direction) is. As you walk, you can maintain a sense of direction for some time ("I was walking towards the north, so it was in front of me, now I turned left, north must be to my right now"). However, since you don't know precisely how much degrees you turned, every turn you make will introduce a small error into your direction estimate, and those errors will add up over time. A couple hours later your sense of direction will have drifted far enough from the original that you might be heading in the opposite direction from where you think you're going. Even if you tried to just walk in a straight line all the time you would probably stray off course eventually, because without external reference you have no way of telling whether you've actually been walking in a straight line (this is known as zero drift).
The only way out of this is to have an alternative source of direction knowledge (e.g. a compass or the combination of the sun's position and time of day, or some other observable directionality in your environment like a distant mountain) which you check regularly and use that knowledge to correct the error in your "internal" sense of direction.
A quadcopter in angle mode has the same problem: to stay upright it needs to know is where "up" is, and a gyroscope can only measure (as an approximation) how much degrees it's been rotated from its previous orientation; it does not know (or care) what that previous orientation was. And even if the FC did know its previous orientation, the estimate might have drifted far off from the original. That's where the accelerometer comes in: its job is to measure the earth's gravity, and therefore the direction of "down", and use that information to figure out the initial orientation when the quadcopter is armed (like knowing where north is when entering the forest), as well as correcting possible drift of the orientation obtained from the gyros in flight. |
H: What is RPM filtering in Betaflight?
I've seen a lot of buzz lately about the supposed advantages of using the RPM filtering option introduced in Betaflight 4.1. What is it and how does it improve inflight smoothness?
AI: Multirotors are inherently a very noisy environment for sensors like the gyroscope which try to measure the actual motion of the drone. Mechanical vibrations and oscillations are present all over, primarily generated by the motors but also by parts in the frame. These vibrations manifest themselves as fluctuations in the gyroscope values.
(cit.)
Flight control firmware relies on a clean measure of how quickly the drone is moving in order to function properly, so they employ a number of techniques to "filter" the gyroscope signal and remove as much of the noise as possible. Unclean signals can result in more inflight oscillations and hot motors. Several different kinds of filters are used, often simultaneously, to accomplish this. (e.g. static & dynamic notch filters, low/high pass filters, Kalman filters) The below image depicting the suite of filters employed by Betaflight helps get across how serious an issue this is, although it isn't quite accurate today. (the image was accurate in some 3.x versions)
RPM filtering (new in Betaflight 4.1) seeks to remove motor noise, one of the most prolific sources of vibrations on a multirotor. The frequency of motor vibrations are directly correlated with their rotation rate, so the Betaflight RPM filter takes input from the ESCs about motor speeds (using bidirectional DSHOT) and uses it to target a series of dynamic notch filters which selectively remove noise from the gyroscope values occurring at a specific frequency. There's a whole page on the Betaflight wiki about this.
Articles like this from Oscar Liang and this on the Betaflight wiki
provide instructions for how to set up and configure the RPM filter, as well as this video from Joshua Bardwell on the topic. |
H: What props for a 2207 2750KV motor?
I have a 4s Nazgul5 drone. It is a 5'' drone and uses 2207 2750kv brushless motors. What is the most aggressive prop I can use on the drone without causing it to overheat or cause the battery to sag?
AI: Things like this are something that is usually only determined empirically, i.e. by trying and seeing what happens. That said, it is unlikely that you will cause damage to your motors by putting too high-pitched of a prop on your drone; racers have been known to put ridiculously high-pitch props on ridiculously high-KV motors and push them to the limit.
Your battery will sag somewhat in almost any case, though. 2750 is already a high KV for 4s; the consensus is that the "sweet spot", middle-of-the-road KV for 4s lies in the 2400-2500 range, and 2750 is towards the "ludicrous speed" side. Putting aggressive props on will add even more to that effect, drawing very high current at high throttle, but also providing very high top speed. So I'd probably advise starting from the lower pitch range, 4.0 and less, and increasing it if the drone flies okay and you feel like you want more.
The question you should be asking yourself, though, is "which prop will feel the best for me on this quad?". Order a bunch of different-pitch props (preferably from the same manufacturer), put up a current readout on your OSD and fly them all in order to see which ones you like best and which pitches strain your system too much. After that you can try out similar-pitch props from different manufacturers to see if they make any difference (i.e. some propellers may be more efficient than others, reducing current consumption).
In the end, the best prop for your drone will depend on a lot of factors besides just the technical specification of your drone, a very big part of which is what you're doing with it (racing, freestyle, long range, fun cruising, etc.), how you do it, e.g. your piloting style, and how you like your drone to feel. |
H: How to clean a drone?
I was just flying my drone when I crashed in some tall grass and there are now a bunch of grass bits all over the drone. How can I clean the drone without damaging it?
AI: I have found that the simplest and probably one of the safest ways is to use a compressor (alternatively a compressed air can will probably work), to lightly blow away the dirt. This works especially well if you just want to get rid of grass straws or similar.
If you want to more thoroughly clean something Joshua Bardwell has a video on how to clean a motor, and if you want to clean a PCB or other electronics, alcohol > 90% and some kind of brush or cotton swab works. And finally, if it's the frame you want clean, soap and hot water works. |
H: How to PID tune a 10" drone?
I have a 10" inch drone that I have trouble tuning. On the default Betaflight PIDs it feels really unstable, and I have tried to raise P, I and D both together and one by one without noticing much difference. Some things I almost doubled even. Since Betaflight is tuned for 5" inch quads (I think); are there more parameters than those three that I should change when tuning a larger quad? Or should I just keep increasing everything?
I should probably also add that I run Betaflight 4.1 with bidirectional dshot and RPM filtering.
AI: Disclaimer: I don't know anything of the following for sure, so be careful. Be very, very careful.
The PID controller itself does not care whether it's a 5 or 10-inch quad. The PID gains, though, do care, and the Betaflight default preset numbers are for something around 5" size. For instance, for a tiny whoop-size quad the gains must typically be raised 3x or more!
I'd imagine this means that for a larger quad the gains should be several times lower than the default, although I have no way of confirming this. In any case, having low PID gains doesn't promote dangerous behavior from the quad, so it's safe to start by cutting the default gains in half or even 3x and working from there. I'd also predict that a bigger quad, having more inertia in both the motors and the frame itself, will need larger feedforward gains to feel responsive than a typical 5".
Another option would be to try and google some published PIDs for a similar-size quad, although that might be a dangerous proposition if you just copy them.
In any case, start from a safe number (it's a 10 inch, so be safe. be very safe) and slowly work your way up. Analyzing the step response in BlackBox logs to gauge the direction in which you need to tune is probably a good idea as well.
The other place you should look at is the filtering tab, as a larger quad naturally has lower characteristic frequencies. It's great that you run RPM filtering, but take a look at the regular lowpass filters as well, you might want to lower the cutoffs for them. You may want to look at your BlackBox logs here as well to decide.
Other than the radically-different gain numbers and possibly playing with the filters, though, the configuration shouldn't be all that different. Good luck, and stay safe. |
H: Video breakup problems with high power using The Force VTX?
I normally fly with my VTX on 200mw but sometimes I need it to be more powerful. Whenever I turn it to a higher power setting, though, the video becomes worse. When I set it to 600mw, the video seems to lose some color and turn black and white at times. Also, very faint lines (white lines, not black lines) appear in the video feed. Does anyone know what the problem could be?
This is happening on BNF 4s Nazgul5. The VTX is The Force VT5804 V2.
AI: This can be caused by too much heat building up in the VTX causing the electronics to suffer. Try mounting the VTX to have more airflow around it or put a heat sink on it. Sometimes a VTX just can't handle its own output power.
Another issue might be that electronic noise from the VTX is getting fed back into the video signal at the camera or FC connection point. Adding capacitors to various voltage rails sometimes can help.
Still another issue could be that the VTX is drawing too much power from the regulator that is supplying it. Try connecting the VTX directly to Vbat if it can take the higher voltage.
In general, noise in the video signal is the bane of FPV video problems. It can be a bit of black magic to fix. |
H: Effect of Deadcat frame on performance?
I've seen a lot of new frames with a Deadcat style because it keeps the props out of view for cinematic videos and such. Does the Deadcat shape of frame have any effects on flight performance?
AI: I personally have never used a Deadcat frame, but I found this forum thread asking a similar question, the answer is:
I was more interested in how the dynamics of a dead cat might affect efficiency. But based on what some of the long-range guys have found, it doesn't appear to be an issue. One thing that did come up with the SG+ at its genesis was instability while in steep dives, like down cliff faces, etc. Guys were setting up in BF as a straight X design. Once they started setting up as a custom in BF and used the program that Project Blue Falcon explains, the instability went away. |
H: Difference between analog and digital FPV systems?
The new DJI digital FPV system and a few other systems are using a digital signal for FPV video. How is this different from a traditional analog signal for FPV drones?
AI: tl; dr:
Analog is:
Cheaper;
Lower resolution;
Has a noisier, more staticky picture that breaks up gradually when the signal gets weaker. Analog image breakup, while unpleasant to the eye, is generally easier to see through.
Has a constant low latency;
Is an entirely open standard, with anyone free to produce compatible equipment
Digital is:
Currently rather expensive,
Has (significantly) higher resolution,
Has a way cleaner image, usually without a speck of static right up to the very limit of its range, but when it starts breaking up, it does so suddenly and in weird ways. The broken image is usually harder to see through than an analog signal. With DJI, for instance, the picture will suddenly get very blocky and low-res when it gets out of range.
Also, digital systems can have inconsistent latency that changes in flight (DJI in particular is known for this), although this mostly concerns the highest-performance pilots, such as racers.
The only digital system currently in widespread use is the DJI system, which is a proprietary standard with only two manufacturers authorized to make the gear.
Analog and digital systems have about the same usable range per unit of VTX power.
To compare how they look, it's better to just see the videos:
DJI HD system range & breakup vs analog
ByteFrost image & breakup
How they work and the reasons for noise/breakup related differences:
Anything that is encoded in a radio signal at a point in time can be represented as a level, which can be higher or lower; Thus the "primary" information encoded in the signal can be represented as a graph of this level over time:
In an analog system that level can take any value, within some range, which we'll think of as 0 to 100% for simplicity(*). It can be 20%, 70% or 48.573498%, theoretically to any degree of accuracy. The drawback to that is that any noise that's floating around in the radio spectrum will add to whatever signal you're receiving, so in practice, you'll get something like 40% (true signal) + 5% (noise) = 45% (received signal), and since the original signal could be anything, the receiver has no way of knowing which part of what it got is noise.
The image that your goggles receive is made up of pixels, and the color that each of them has is encoded as percentages of red, green and blue: zero to 100%. An analog TV system encodes this picture by "scanning" over all of the pixels in sequence, line by line, and setting the signal's level equal to each pixel's brightness in turn. For example, this oscilloscope picture represents the TV signal for the "colored bars" picture:
The ladder you see represents how the brightness level of the pixels changes from left to right in each line of the image.
There are also other signals overlaid on top of it, these correspond to the lines closer to the bottom of the image, which have other sequences of colors in them (the oscilloscope displays all the lines together on one screen).
The consequence of all that is that whenever there's another signal on your frequency around, it gets added to your VTX's signal and through that directly to your picture. Since usually that other signal is noise(**), your picture is overlaid with noise.
When your signal is strong, the noise is a very small percentage of it and is usually unnoticeable by the eye. As the useful signal gets weaker, though, the noise (which stays the same) will get stronger compared to it, so the percentage of noise in your picture increases. At some point, it will become so strong that you couldn't see any useful signal in the picture anymore.
In a digital system, however, only two levels are available: 0 and 1, represented by 0% or 100%(***). The image is encoded into a sequence of bits using a special algorithm, called a codec, and decoded from that sequence on the other end, almost exactly like online video. Besides simply encoding the video feed, one of the most important functions of modern codecs is to compress it, so that it can be communicated in a significantly smaller amount of bits, which in turn means that higher-resolution video can be transmitted with the same bitrate (number of bits sent per second).
Since radio signals are by their nature analog, on the receiving end noise will still be added to the signal, so if a 0 was transmitted and 10% of noise is added by the environment, the received result is 10% — but since the receiver knows that only either 0 or 100% could have been transmitted, it picks the closest possible level, in this case, 0.
This means that when you transmit digital data, noise is just ignored until a certain point: Even when noise levels are as high as half of the analog signal (which creates a picture that's rather hard to parse), with digital you receive exactly the same information as you would if there were no noise, with the resulting video perfectly clear. However, when the relative noise level does pass the critical threshold, ones will start suddenly (and randomly) becoming zeroes and vice-versa. What happens to the video after that depends on the particular digital system and how the video is encoded in it.
With the DJI system, the whole screen suddenly becomes low-res and blocky, occasionally skipping frames, and the latency increases. The cumulative effect of this can range from "just an unpleasant-looking image" to "totally unflyable".
With Fatshark's Bytefrost system (currently in development/beta testing), random bits of the image will flash with colored blocks, while the rest remains high-resolution. The manufacturer touts this "analog-like" style of image breakup as a feature of the system.
In both cases, digital breakup, when it does happen, is arguably harder to see through than analog breakup, because our brain still has better error correction software than seen in these systems. This is also due to the fact that digital images, while crystal clear up to a point, start breaking up sharply after that point and quickly get to "very hard to parse" levels, while an analog picture is already quite static-ridden by then and just continues to gradually get worse.
That said, digital systems can employ error-correcting codes and other tricks to be able to recover from a certain percentage of errors, at the expense of reduced bitrates, yielding a lower-quality image which can be decoded from a longer distance. you'll typically see them start to gradually reduce image quality before breaking down completely, giving you some warning signs that you are going out of range. There is also usually a link health indicator somewhere in the corner that is similar to the RSSI reading for RC control systems which you could look at to see if you're going out of range. You probably aren't going to be looking at it all the time, though, and a low signal indication can be missed, while it's hard to miss an image full of static and getting worse.
Footnotes:
(*): The analog signal can technically be any real number, and can sometimes go beyond its designated range, i.e. in our example be less than 0 or bigger than 100%. How the system handles the signal going out of its designated boundaries is the system's business.
(**): the other common kind of interfering signal is your own signal that's reflected off of something. In which case you will get two of the same picture overlaid on top of each other, but one of them which is slightly late and is shifted to the right because of that. This is called multipath interference, or multipathing, and is a major source of image degradation with analog FPV systems. Cutting down on multipath signals is also the primary reason why circular-polarized antennae are used in FPV..
(***): Actually, a digital system can have more than two values, and there are different ways of representing them as analog levels; the main distinguishing factor is that there's a fixed (integer) number of them. For example, for a simple digital system with 4 levels, they would be 0, 33%, 66%, and 100%, with corresponding ranges of -∞ to 16%, 16-50%, 50-83%, and 83%-∞. |
H: How hot should an ESC get?
What is the maximum safe temperature that a brushless drone ESC should get? What could happen if a brushless ESC were to go over its maximum temperature tolerance?
AI: It really depends on the ESC. Different ESC's have different ratings.
Many ESCs would perform best under 85°C and some microcontrollers work better if under 70°C. But there are ESCs that can work just fine with hotter temperatures. For example, Castle Creations ESCs can handle a sustained 70-82°C and will have issues around 100°C but most ESCs will have lower tolerance levels and may have issues above 80°C. In general, the closer an ESC is to room temperature, the better it's longevity will be.
If an ESC gets too hot, several things could happen that would result in it burning out. Some components of the ESC could stop functioning.
So the best thing you can do is look at the temperature ratings for the specific ESCs you are looking at and measure the temperature of the ESC after a flight. If the ESC is too hot you can set a throttle limit or adjust power in some way.
There is some more information here. |
H: When to replace bearings in a brushless motors?
When, if ever, should I replace the bearings in my drone's brushless motors? Are there signs that a motor needs new bearings?
AI: Bearings generally last much longer than the rest of the motors with how often we crash. If you notice a rougher noise or the motor doesn’t feel smooth when you spin it, that’s a sign your bearings might be shot. |
H: Difference between iFlight XING-E and XING motors?
Is there any performance difference between iFlight's XING-E and XING lines of motors? I know that the XING motors have some better materials like titanium shafts but are there any performance differences?
AI: The Xing and Xing-E motors have two primary differences, materials used in the bell construction, and the magnets used. The bell is a lower stength 6061 aluminum alloy than what they claim for the Xing primary line. Also, even though all motors tend to claim "N52SH" or "N52H" magnets in their specifications, there is a huge range of variation in magnet strength between brands and lines. The magnets in the E series appear to be a bit thinner than the standard line counterparts, but likely they are a tier lower in rating. The full Xing line also has either a two piece or single piece (machined as part of the top of the bell) aluminum cover surrounding the flux ring, depending on which version and when you purchased it. As you mentioned the Xing motors have a titanium alloy shaft while the Xing-E have a hardened steel shaft.
As far as performance differences go, yes there will be a performance difference. Differences in magnet strength and manufacturing tolerances mean the Xing line has more torque and higher thrust than the Xing-E motors. The difference is not going to be drastic however. The Xing were fairly conservative, coming in a bit under the stated Kv. I haven't tested the Xing-E in the bench yet, but I have done a few builds for friends with them and had them up close to compare.
Check out the details on the Xing here: https://www.miniquadtestbench.com/iflight-xing-2306-2450kv.html
I'll try to borrow a spare Xing-E from my friend who I did a build for and see if I can get it for comparative data. I'll update here if I can get it. |
H: Why do brushless drone motors tend to be more expensive than brushed?
The most common motors used for modern drones are brushless outrunner motors and I have heard that they are simpler to manufacture and are less susceptible to issues when being mass-produced than brushed motors because the only parts of the brushless outrunner that rub together are in the bearings (they don't require a brush to be at just the right spot or pressure or anything). If this is the case, why do brushless motors tend to be more expensive than brushed motors?
AI: Brushless motors are typically CNC machined for a large part of their manufacturing process. The top part of the bell and bearing race are machined from aluminum. The shafts typically steel or a titanium alloy and are CNC machined in a lathe. The steel flux ring is typically pressed, and the stators are stamped from existing templates for the most part. The machining is somewhat expensive comparatively, the stamped and pressed parts are relatively inexpensive compared to the other costs involved. In general, it's a fairly complex manufacturing process, and the materials are not necessarily the cheapest. The cost goes down as volume goes up, and a lot of what we use in the DIY drone industry is fairly small batch production, which helps drive up the cost. There's also the supply and demand question and to a certain extent, the cost is set by what the market is willing to pay. That being said I personally know a lot of brushless manufacturers, and the race to the bottom on prices that we're seeing in certain parts of the hobby (low-cost FPV motors) are pushing the absolute limits of the margins.
Brushed motors, on the other hand, have essentially no CNC'd parts, almost everything is pressed or stamped including the can. Average quality brushed motors with average tolerances and efficiency are cheap and easy to produce. The cost with brushed motors comes when you need to increase precision, performance, and efficiency. However the advent of reasonably priced brushless motors has pretty much nullified that market, so all we're left with us the first category except in very narrow niche applications, none of which I've had the occasion to explore yet. |
H: Isn’t flying FPV drones illegal accoding to FAA rules?
I understand there is First Person View (FPV) drone flying which involves putting on a headset and controlling the drone from the live camera feed,
The FAA Rules For Unmanned Aircraft Part 107 state:
Visual line-of-sight (VLOS) only; the unmanned aircraft must remain within VLOS of the remote pilot in command and the
person manipulating the flight controls of the small UAS.
If that is true, then surely FPV flying is illegal as you don’t maintain a visual line of sight with the aircraft?
AI: FPV is not actually illegal because that document also states:
Part 107 does not apply to model aircraft that satisfy all of
the criteria specified in section 336 of Public Law 112-95.
and the criteria specified in section 336 of Public Law 112-95 is:
(1) the aircraft is flown strictly for hobby or recreational use;
(2) the aircraft is operated in accordance with a community-based set
of safety guidelines and within the programming of a nationwide
community-based organization;
(3) the aircraft is limited to not more than 55 pounds unless
otherwise certified through a design, construction, inspection, flight
test, and operational safety program administered by a community-based
organization;
(4) the aircraft is operated in a manner that does not interfere with
and gives way to any manned aircraft; and
(5) when flown within 5 miles of an airport, the operator of the
aircraft provides the airport operator and the airport air traffic
control tower (when an air traffic facility is located at the airport)
with prior notice of the operation (model aircraft operators flying
from a permanent location within 5 miles of an airport should
establish a mutually-agreed upon operating procedure with the airport
operator and the airport air traffic control tower (when an air
traffic facility is located at the airport)).
This is essentially saying that if it is a recreational drone, follows community guidelines, is not more than 55lbs, doesn't interfere with manned aircraft, and notice is given to airports before flying within 5 miles of them, that FPV is perfectly Legal |
H: Drone “fine tuning”
On my controller for my drone there are 4 buttons:
Forward fine-tuning
Left fine-tuning
Back fine-tuning
Right fine-tuning
What is “fine-tuning” and how does one decide what direction to “fine-tune” in?
AI: Generally, the term for this is "trim". It is used to slightly adjust the center position of the stick on a controller. If the craft is moving slightly to one direction without you putting any input to the controller, then you would adjust the trim for that stick so that the craft remains stable without stick input. These adjustments are more commonly needed on RC planes without a flight controller to adjust for slightly off control surface servos. It can also be used to correct for a drifting gimbal in the controller. |
H: Recommend safe distance from other drone flyers
When going to fly my drone, I notice there are a few other drone flyers as well.
What is the recommended safe distance to be kept from other drone users in order to not cause an accident?
AI: In this situation, I would approach the other flyer(s) to say hello and discuss this with them to prevent misunderstandings or differences of opinion - for example, if the other flyer is new they might want much larger separation than you think is enough, whereas if you are both experienced you might be happy flying in close quarters.
Also, it might make life easier if you stand close to each other; I've done this before (albeit with people I knew) and it is useful to regularly share information like "I'm at 200 ft by the tree on the left", "Thanks, I'm at 50 ft moving across to the right" - and of course warnings like "Unleashed dog approaching!" and "Helicopter!"
If you are looking for official guidance, you could check CAP 393 Article 95:
95.—(1) The SUA operator must not cause or permit a small unmanned surveillance aircraft to be flown in any of the circumstances described in paragraph (2), and the remote pilot of a small unmanned surveillance aircraft must not fly it in any of those circumstances, except in accordance with a permission issued by the CAA.
(2) The circumstances referred to in paragraph (1) are—
(a) over or within 150 metres of any congested area;
(b) over or within 150 metres of an organised open-air assembly of more than 1,000 persons;
(c) within 50 metres of any vessel, vehicle or structure which is not under the control of the SUA operator or the remote pilot of the aircraft; or
(d) subject to paragraphs (3) and (4), within 50 metres of any person.
(3) Subject to paragraph (4), during take-off or landing, a small unmanned surveillance aircraft must not be flown within 30 metres of any person.
(4) Paragraphs (2)(d) and (3) do not apply to the remote pilot of the small unmanned surveillance aircraft or a person under the control of the remote pilot of the aircraft.
(5) In this article, “a small unmanned surveillance aircraft” means a small unmanned aircraft which is equipped to undertake any form of surveillance or data acquisition. (b)
I am not aware of any specific rule for separation in relation to other drones, unless they were to be considered a vehicle for rule 95(2)(c) in the quote but elsewhere in CAP393 they use "flying machine" to refer to (any) aircraft.
However, as always, there is the 'catch-all' in Articles 94 and 241 should something go wrong:
94.—(1) A person must not cause or permit any article or animal (whether or not attached to a parachute) to be dropped from a small unmanned aircraft so as to endanger persons or property.
(2) The remote pilot of a small unmanned aircraft may only fly the aircraft if reasonably satisfied that the flight can safely be made.
(3) The remote pilot of a small unmanned aircraft must maintain direct, unaided visual contact with the aircraft sufficient to monitor its flight path in relation to other aircraft, persons, vehicles, vessels and structures for the purpose of avoiding collisions.
and
A person must not recklessly or negligently cause or permit an aircraft to endanger any person or property. |
H: Does the performance of a brushless motor decrease over time?
The brushes wear out in brushed motors and their performance decreases until they stop working, but brushless motors have fewer parts in contact and thus don't wear out nearly as fast.
Does the performance of a brushless motor decrease over time or does its performance remain practically the same throughout its life?
AI: Like most things, it depends on how you treat it.
As far as I know, you should never need to worry about a brushless motor wearing out, especially for our purposes where we will likely demolish them before they have a chance to wear out.
You do have to watch out for the bearings and magnets, however.
With the bearings, like any mechanical component, they will eventually wear down, however this will likely not be for a long time. It is still a consideration, though.
You also have to watch out for the magnets.
Under normal circumstances, the magnets are fine to last a long time, however excessive heat can eventually demagnetise them, leading to reduced performance and eventually the motor not producing enough power for us to use.
If anyone has any other ideas or wants to correct me, please do! |
H: What's the purpose of airmode and idle up?
What are airmode and idle up and what do they do improve my freestyle flights?
AI: Airmode and idle up both seek to increase a control authority and stability during ultra-low throttle moves.
In normal flight, when the pilot commands the multirotor to pitch or roll (cyclic), the flight controller responds by increasing thrust on one side of the craft and decreasing thrust on the other side by the same amount proportional to the cyclic rate commanded. This symmetrical change in thrust allows for quicker rotation than would otherwise be possible if the flight controller only increased power on one side.
The trouble comes when a pilot tries to change the attitude of the multirotor when the throttle commanded by the pilot is near zero (min_throttle). The flight controller obviously can't decrease the speed of a motor below zero (aka. idle speed), so it has to do something to ensure it can achieve the cyclic rate the pilot wants. Without anything to fix this behavior, the flight controller would only respond with as much as it could without making any motors increase thrust more than the others can decrease thrust. This results in massively decreased control authority at low throttle because the flight controller can only provide minuscule adjustments to motor thrust.
This is where idle up and airmode come into play, although they solve the problem a bit differently.
Idle Up
Idle up is setting configurable in the RC transmitter which changes the throttle curve at the low end so that it the bottom-most throttle position doesn't actually correlate to the transmitter sending zero throttle to the multirotor. Instead, it would send some low value that you configure, usually below 10%.
This would allow the flight controller to speed up and slow down motors by the amount you configure for the increased idle speed, which is a lot better than what it could otherwise accomplish at low throttle.
Airmode
Most modern flight controller firmwares support airmode, including Cleanflight and Betaflight.
When enabled on the flight controller and the pilot commands a large rotation while at low throttle, the flight controller temporarily pretends that the pilot's throttle command is high enough for it to slow down motors to zero throttle and still achieve the cyclic rotation rate the pilot wants. When the pilot commands less cyclic rotation rate, the flight controller stops pretending that the throttle command is higher than it actually is.
For a graphical explanation of this functionality on paper, I recommend taking a look at Joshua Bardwell's video about airmode.
To see what this looks like visually during low-throttle maneuvers, I recommend watching Le Drib's video about idle up vs. airmode. (link starts at relelvant section) |
H: How are Hall effect gimbals different than standard gimbals?
I know that hall effect gimbals are supposed to be better than standard gimbals and are seen on a lot of expensive transmitters. What are the differences between a Hall effect gimbal and a standard gimbal?
AI: The difference is in how the gimbal position is sensed and reported to the processor in the transmitter. The two main types are potentiometer and hall effect gimbals, but in both types, the fundamental mechanism holding the gimbal and allowing it to rotate is the same.
Potentiometer (aka. pots)
Potentiometers are resistors which change their value depending on the location of the wiper along the resistive strip inside them. In a RC transmitter, the wiper is connected to each axis of the stick. The processor in the transmitter reads an analog voltage from the potentiometer and translates that to the axis' value.
(cit.)
Hall Effect
A hall effect sensor also reports an analog voltage, but this time based on the strength of the magnetic field it senses. A magnet is attached to each axis of the gimbal and a hall effect sensor is placed on each side of the frame of the gimbal. The movement of the magnets either closer or further from the hall effect sensor registers as a changing value for the axis.
Comparison
Potentiometers are generally less precise than hall effect sensors and tend to drift over time, leading to a need to calibrate the center point of each axis every once in a while. This doesn't need to be done with hall effect gimbals. |
H: What propellers should I get for my drone?
How do I know what type of propellers to get for my drone and what do the specific numbers for each propeller mean?
AI: The first step to getting the right propellers is to figure out what size propellers will fit your drone. What you can do is measure the distance from the center of the motor to the closest thing (probably the frame) that would block the propeller. Multiply that by two, and a few millimeters smaller than that is the maximum prop size/diameter. (smaller props can also work)
For example: if the center of a motor is 2.6 inches away from a frame, I would get 5'' props.
The next thing to look at is the pitch and number of blades. This is where most of the numbers come in for props. Let's use the example of 5143. the first part, 51, is the prop diameter (5.1'') and the second part is the pitch of the prop, 43, which would mean that the pitch of the prop is 4.3''. A higher pitch generally uses more power but can result in faster flying to some extent. (sometimes the prop pitch is not entirely accurate, as it depends on what the manufacturer thinks) The number of blades of the prop will be listed separately when the dimensions of the prop are listed like this.
Another way you may see prop dimensions formatted is like this: 5.1x4.3x3. That essentially says the same thing except it also includes the number of blades, which in this case, is 3. The 5.1 is 5.1'' diameter and the 4.3 is 4.3'' of pitch.
What I would recommend is to try many different types of propellers because many props that have the same measurements will perform differently. |
H: Why don't multiprotocol transmitters work with Radiolink receivers?
I have a Jumper T16 and am wondering why it or any other multiprotocol transmitters don't work with Radiolink receivers. Is there a reason for this?
AI: The Jumper T16 multiprotocol module doesn't support Radiolink receivers, as you know. This is because the module doesn't have any hardware to recreate the Radiolink protocol.
As can be seen on the product listing for the T16 Pro here,
RF Chip Data
Cypress Semiconductor CYRF6936: DSM/DSMX, Walkera Devo
Texas Instruments CC2500: FrSky, Futaba SFHSS
Amiccom A7105: FlySky, FlySky AFHDS2A, Hubsan
Nordic Semiconductor NRF24L01: HiSky, Syma, ASSAN and most other Chinese models
The reason for this is likely either that:
The necessary hardware to create the Radiolink protocol either isn't available to third parties or isn't cost-effective to license
Radiolink receivers aren't popular enough to warrant the R&D required to reverse-engineer the protocol or include in a radio |
H: Why do a quadcopter's opposite rotors spin in the same direction?
All the quadcopters I've seen have four motors, arranged in a square-like shape. Two of these rotors spin one way, and two of them spin the other way so that the main body of the quadcopter doesn't rapidly spin as it flies. (Conservation of angular momentum.)
I find it interesting that the two rotors that spin in the same direction are opposite, not adjacent. Why not put the two anticlockwise-spinning rotors on one side and the two clockwise-spinning rotors on the other side? That seems the natural way to do it.
So what makes the opposites-spin-the-same design better?
AI: This design is to prevent unwanted yaw when moving, or vice-versa.
Consider the following two actions:
When a quadcopter yaws, it does so by creating a speed difference between the opposite-rotating rotors; creates a torque that rotates the quad.
When a quadcopter moves left/right, it does so by slowing all the motors on one side of the frame and/or speeding those on the other, imparting a slight roll - the thrust is now slightly sideways, so it moves. (This is the same for front/back.)
From this, you can infer that if the same-direction rotors were on the same side as each other, when creating a speed difference to yaw the aircraft you would also impart a roll. Similarly, when trying to roll the aircraft would yaw.
The image below shows visually how an opposite-corner rotation quadcopter moves: |
H: How does a propeller with more blades create more "grip"
I have heard that the more blades a prop has, the more "grip" it has in the air at the expense of speed.
How do more blades create more grip but lose top speed?
AI: Aside from fancy material science which can result in propellers that interact with air more cleanly and is highly proprietary, the primary way a propeller could gain more "grip" on the air is by being more aggressively pitched or having more blades.
In a propeller spec which can be displayed either as:
[diameter in tenths of an inch][pitch in tenths of an inch], e.g. 5042
[diameter in inches]x[pitch in inches]x[number of blades per prop], e.g. 5x4.2x3
the pitch of the propeller theoretically represents how far forward the propeller would move over the course of one rotation if it were curring through a solid material. More aggressively (higher) pitched propellers can be said to "grip" the air more than less aggressive pitches because they will go further per rotation.
The same is true for high blade count propellers, which will also go further per rotation due to the fact that there's more surface area for air to exert a reaction force against.
But I think that the idea that propellers need to trade increased pitch and increased blade count for rotation speed is technically wrong. Just like how saying that higher kV motors require lower-voltage batteries isn't technically correct but in practice holds true, I believe the same holds true for propellers.
It is true that aggressively pitched and higher blade count propellers require more powerful motors to drive because they do more work per rotation. This is the reason why in practice these propellers are usually paired with lower-kV motors which spin slower per volt because they require less rotational velocity to do the same amount of work.
It should be noted that some (well-designed) propellers mitigate the increased work required to spin propellers with more than three blades by decreasing the chord length of each blade, thus decreasing the area of the blade and the work required to rotate it. This is where reading the spec sheet of the propellers you want to use and taking a careful look at the aerofoil geometry is key. :)
(cit.)
However, nothing would stop you from pairing a high-voltage battery with a high-kV motor and an aggressively pitched propeller with many blades. The setup would, of course, consume ungodly amounts of power and require some pretty special materials to ensure the propeller doesn't shatter from the intense forces it would feel at those high speeds, but it could technically be done and there isn't anything wrong with doing so. |
H: How to update the firmware of a T16 Pro's internal multiprotocol module?
How should I go about updating the internal multiprotocol module firmware of my Jumper T16 Pro?
AI: The first thing to do is to check that you have the bootloader. Newer radios should have it installed. (Just check that you have Multiprotocol Module firmware v1.2.1.85 or later) If you don't have the bootloader installed, here is a video on how: Jumper T16 "Update Recommended" Fix (how to flash internal multiprotocol module).
Assuming you have the bootloader, the next step is to go here: MULTI-Module Firmware Downloads. Here, you can get the latest firmware for any multiprotocol module, so this works for more than just the T16. On the left, find the module that you want to update. In this case, the Jumper T16 Pro Internal module.
After that, most of the information is filled out so just fill in the rest (in this case just channel order)
Get the file that corresponds to the channel order of your radio:
Put the file onto the FIRMWARE folder of the micro SD card from the Jumper T16 and then put the card into the T16 and power it on. Long press the system key, press the page button once, scroll down to [FIRMWARE] and click it, long-press the new file, and then Flash Internal Multi.
If you need a more comprehensive guide, check out Joshua Bardwell's video: Jumper T16 "Update Recommended" Bootloader Method (how to flash internal multiprotocol module). |
H: How to drive a servo for a tricopter with a flight controller?
Is there any way to set up a servo with full control for a tricopter using a normal flight controller and normal drone parts? Are there any other things that I should use or consider?
This servo will be used to roll the rear motor (there will be two front motors). The prop size will probably be around 6-7'' so the servo will require a decent bit of power.
Essentially, I'm asking if a servo can be powered from a flight controller (does the flight controller have the ability to output 3a 5v) and can I control the servo? Are there only specific flight controllers that can output that?
AI: This has likely been answered here: https://drones.stackexchange.com/a/230/50, but to paraphrase:
A standard flight controller can easily be set up to control a servo, as per your edit.
You first need to plug in your flight controller (with props off, if you’re using one with motors already attached) and enable ’servo tilt’ in the configuration tab, then go into the CLI.
You then need to type ‘resource’ (assuming you are on the latest version of Betaflight.)
As you want a tricopter and your flight controller is likely for a quadcopter at least, you can reassign a motor output (or any other PDB with a built-in timed) to become a servo output. If you don’t know how to re-map resources in Betaflight, the answer I have linked gives an excellent rundown.
You should then see a servo tab appear in Betaflight, and from there you should be able to configure everything you need. |
H: What happened to DSHOT1200 support in Betaflight?
I just went to update my flight controller from 3.5.3 to 4.1.0, and I noticed that some time in the past two years the option to enable DSHOT1200 was removed from Betaflight.
Does anyone know why this happened? Was it something to do with the release of RPM filtering?
AI: As is explained in this forum post, support for DSHOT1200 signaling was indeed removed from Betaflight due to its primary use case being devalued starting in version 4.1.
DShot1200 is officially removed from Betaflight 4.1:
Dshot1200 is only needed for 32khz looptime, and 32khz looptime isn't supported any more in Betaflight. The highest looptime in Betaflight (in BF4.1) is 8KHz, and Dshot600 is enough for 8khz looptime
Dshot1200 was not stable when used with bidirectional DShot which is required for RPM filter, which has a higher priority than DShot1200
This GitHub issue also points out that DSHOT1200 was poorly supported by BLHELI_S and BLHELI_32 ESC firmwares and wasn't really necessary to maintain. |
H: Can you cancel an automatic landing triggered by a low battery on the Dji Mavic 2 Pro?
Whenever the DJI Mavic 2 Pro has a low battery it initiates a function that lands it. Sometimes this can happen when the drone still has a lot of battery capacity e.g. 45%.
Is there a way to cancel this return to home function?
AI: If you have more then enough battery, you can disable it as stated in the manual:
Low Battery RTH
Low Battery RTH is triggered when the Intelligent Flight Battery is depleted to the point that the safe return of the aircraft may be affected. Return home or land the aircraft immediately when prompted. DJI GO 4 displays a warning when the battery level is low. The aircraft will automatically return to the Home Point if no action is taken after a ten-second countdown. The user can cancel RTH by pressing the RTH button or Flight Pause button on the remote controller.
Note: this function is intimated specifically so the drone has enough battery to come back to you, so if you cancel it, make sure you know what you’re doing.
The function can not be overridden if the drone only has enough battery to descend from its current altitude:
The aircraft will land automatically if the current battery level can only support the aircraft long enough to descend from its current altitude. The user cannot cancel the auto-landing but can use the remote controller to alter the aircraft’s orientation during the landing process. |
H: Advantages to having more rotors?
I have a quadcopter drone, is there an advantage say of having a octocopter instead of a quadcopter. Will it improve performance?
AI: Performance is unlikely to be improved, in terms of speed or agility, or even load-bearing capacity, as they are heavier, slightly less efficient aerodynamically, and more expensive.
What you do get is a degree of fault-tolerance.
With a quadcopter, losing one rotor means your drone will fall out of the sky. With an octocopter (or hexacopter, but an octocopter can lose more motors and still be able to fly) losing one rotor is not fatal - it will still fly, however, it will have a reduced control authority.
This makes them very desirable for carrying expensive loads - such as a £50,000 camera - you really don't want to drop that out of the sky if you have a fault. |
H: Differences between fiberglass-reinforced plastic and polycarbonate propeller materials?
What are the differences between drone props that are built from fiberglass-reinforced plastics and props made from polycarbonate?
AI: The main differences are:
Fiberglass-reinforced plastics: Very stiff for their weight which allows the propeller to keep the correct shape and be more efficient regardless of how fast it spins (less prop flattening), but when these props hit something hard, that stiffness means it will shatter and the drone won't be flyable. Fiberglass-reinforced props are also not very susceptible to heat which is good and means that they will continue to be rigid and efficient in very hot weather. The brittleness of these props means that it is not likely you will be able to use Turtle Mode successfully very often.
Polycarbonate: Good stiffness and will bend rather than break if it hits something hard. This means that when you crash, a blade may bend rather than break and can often be bent back into shape. Polycarbonate props, however, are susceptible to temperature and will become brittle and can shatter if it is very cold and can become soft and not efficient of it gets too hot. |
H: How do I set up the RSSI readout on an XM+ receiver channel?
I have an old XM+ receiver that does not do RSSI. Some of the newer ones come with RSSI set up on a channel. How can I set up RSSI to be on a certain channel?
AI: For the sake of the random visitor I must first point out that the XM and XM+ receivers do not include telemetry, as in they don't transmit anything back to your remote over the radio link. What the XM/XM+ do offer, however, is an onboard RSSI readout, i.e. supplying RSSI information directly to the flight controller.
These receivers have two ways of communicating that readout.
The first is the RSSI pad, indicated on the schematic in the receiver's manual.
You can solder a wire to this pad, and it will output the RSSI value as a voltage which can then be read by your flight controller via an ADC pin (usually labeled RSSI). This feature is, as far as I know, always on.
The second, which is the one you're asking about, is transmitting the RSSI readout as one of the RC channels, either channel 8 or channel 16.
To enable the latter option (if it's not enabled) or change the channel, you'll have to flash the corresponding firmware to the receiver. If you go to the FrSky site, to the page that offers firmwares for your receiver, and download the archive, you'll see six files, labeled something like:
XM+FCC170313.frk
XM+FCC170313-RSSI16.frk
XM+FCC170313-RSSI8.frk
XM+LBT170313.frk
XM+LBT170313-RSSI16.frk
XM+LBT170313-RSSI8.frk
The files ending in RSSI8/RSSI16 are the ones you need to flash to enable RSSI readout to the corresponding channel; the ones without any suffix have this feature disabled, if you want all the channels as actual channels and use the analog RSSI readout. Also remember to flash the RF option (FCC or LBT) that matches your transmitter, to avoid possible issues when binding.
After flashing, you'll have to rebind the receiver and configure your flight controller to correctly read the RSSI. In betaflight you need the RSSI_ADC option to be enabled to use the first option (analog readout), and you need it to be disabled to use the RSSI-on-a-channel feature. As long as you have the RSSI_ADC option enabled, the RSSI channel setting in the receiver tab won't be saved when you set it. |
H: Difference between T700 carbon frames and 3k carbon frames?
I have heard that iflight's Green Hornet uses T700 carbon instead of 3k carbon. What difference does the new T700 carbon make?
AI: First of all, the 300 or 700 is the grade value of carbon fiber and generally, a higher grade means more strength and better performance. The main differences between T300 (3k) carbon and T700 carbon are that T700 carbon has almost 40% more tensile strength than 3k carbon, T700 carbon is slightly denser (and thus heavier for the same volume of carbon), T700 carbon fiber has a higher carbon content and a lower nitrogen content, and T700 carbon fiber is smoother looking while T300 carbon looks more bark-like.
So, overall, T700 carbon is better for making a drone frame because it is significantly stronger with only a small increase in weight. |
H: How does a quadcopter flip without falling very much?
I have a quadcopter and it has a flip function (as do many other quadcopters).
I was wondering how this works. Say I am flipping it right (clockwise), I assume the motors on the left spin much faster than those in the right. If so, how does the quadcopter not loose too much altitude when doing this?
AI: The trick is speed. The reason why multirotors don't lose (very much) altitude while performing quick mid-air aerobatics is because of the speed of the move and the skillful management of throttle by the pilot.
You're correct in presuming that a multirotor performs a flip by changing the speed of the motors on each side of the craft. Freestyle pilots usually make use of near-total stick deflection and extreme rate profiles targeting ~600-1200 deg/s of angular velocity. The fact that the flight controller speeds up motors on the side which needs to rotate "up" and slowing down those on the side which needs to rotate "down" ensures that the move occurs as fast as possible because all four motors contribute to the torque which rotates the multirotor.
The other factor which helps the multirotor not descend too much is the skillful management of the throttle during the move. By lowering the throttle to near idle while the craft is inverted, the pilot minimizes the amount of thrust the craft generates which acts to pull it down towards the ground. As I discuss in my answer to "What's the purpose of airmode and idle up?", the idle up and airmode features (of the RC transmitter and flight controller respectively) help ensure that the multirotor is in control during these times of low-throttle.
Because of these two factors, the duration in which gravity has the power to suck the craft towards the ground is often too little to matter, and the multirotor flips in-place.
Of course, there's nothing preventing you as the pilot from slowing down the flip and performing an "O"-shaped loop instead of a flip in-place. This can be done by easing off the roll/pitch axis and turning down rate profiles. |
H: Why is 5.8ghz used for FPV and 2.4ghz use for transmitters?
Why do most VTXs use 5.8ghz and most transmitters use 2.4ghz?
AI: As is discussed in this Oscar Liang article, FPV hardware exists for all different kinds of frequency bands, stretching from 900 MHz to 5.8 GHz, with 5.8 GHz being the most popular today. People in our hobby have tried nearly everything under the sun. :)
Probably the most well-known tradeoff in RF is that between frequency and penetrating power. In general, higher frequency transmissions will not be able to travel as far and penetrate as many obstacles as lower frequencies.
This would make it sound like lower frequencies would always be better, but this is not the case. Especially in the case of FPV video, available bandwidth and interference issues become more of a concern than pure range.
With increased frequency comes higher bandwidth and reduced latency, which is to say that the 5.8 GHz band accessible to us can support more data throughput at a lower latency than the 2.4 GHz band. This is critical because video transmission requires several orders of magnitude more data to be sent than RC controls and telemetry do because it sends entire pictures instead of a few numbers per transmission.
The Troubles With 2.4 GHz FPV Radios
The need for more bandwidth in the 5.8 GHz range is further compounded by the fact that our analog FPV systems usually aren't frequency-hopping. In the old days of the RC hobby when airplanes were the only option, most RC transmitter/receiver systems had a fixed operating frequency. I have a couple of these transmitters, which actually have a slot where you need to insert a special crystal oscillator to select which frequency the transmitter uses!
This became a problem once people started coming together to fly and the RC hobby became more widespread. All of a sudden, people would begin turning on their transmitters at the flying field and their transmitter would talk over other people's transmitters using the same frequency, blasting them out of the sky and interrupting the controls to their plane. (does this sound familiar? XD) This issue was worsened by the fact that the 2.4 GHz band we are allowed to use doesn't allow for very many non-overlapping channels and because the 2.4 GHz band is used by many other different kinds of devices and appliances which can also step on RC transmitters' signals.
The solution to this problem, which has been implemented in the vast majority of all 2.4 GHz RC systems, is to implement frequency-hopping. This feature allows the RC system to dynamically switch between frequencies on the fly as needed, without any input required from the pilot.
These same issues caused by transmitters stomping on each others' signals are also a massive issue in the 5.8 GHz band, but to a far lesser extent due to the vast array of different non-overlapping channels available for use.
(cit.) |
H: Difference between XM and XM+ receivers?
I have seen both XM and XM+ receivers and am wondering which one would be better to get for a micro-drone build. What are the differences in specs? (range, reliability, weight, etc)
AI: According to Oscar Liang, the XM+:
Is larger and heavier than XM (21.5 x 12 x 3.5 mm – 1.6 g)
Has diversity antennae, unlike XM
Has solder pads in addition to pin headers
Doesn't support Smart Port telemetry
Has RSSI channel support on a dedicated pad and 16th channel
Has a wider input voltage range than XM (3.7v-10v) |
H: What is DSHOT in ESCs?
I've heard that modern quadcopters use a DSHOT protocol. Could you describe what it is?
What's its purpose?
AI: DShot is a protocol that flight controllers use for communicating with ESCs. It stands for 'Digital Shot'. It is a new digital communication protocol developed by Flyduino in collaboration with Betaflight as an alternative to Oneshot and Multishot.
Oneshot and Multishot (and standard PWM) all use analogue signals. The length of an electrical pulse determines the value being sent from the flight controller to the ESC. This can lead to problems with accuracy if there are slight differences between the speeds of the clock signals in the ESC and the flight controller (which is why ESC calibration is required with analogue protocols). Also, these signals have a fixed length range of 1 to 2 milliseconds, which means they can't be sent more often than once every 4 ms or so, or 250 times a second.
Digital signals can also be more resilient in the presence of electrical noise.
The number associated with the protocol indicates how much data is sent per second. There are several speed options available:
DShot150 – 150,000 bits/Sec
DShot300 – 300,000 bits/Sec
DShot600 – 600,000 bits/Sec
DShot1200 – 1,200,000 bits/Sec |
H: How to recognize damaged brushless outrunner motors?
I would like to know how to recognize damaged brushless motors on a drone? What are the most common symptoms?
AI: There are many signs that a brushless motor is broken or getting worn out. Something that can happen to motors that have been used for a long time is their bearings wear out. If you notice that the bell of a motor feels loose or the motor is excessively noisy or has a grinding sound, it is likely worn-out bearings. You can either replace the bearings or buy a new motor.
Another thing that happens is the magnets can demagnetize over time if the motors get hot. A way to know if this has happened is to run the motor with no load. If the RPMs are unusually high, the magnets are likely losing their strength. In this case, you need a new motor. |
H: Where do we download Betaflight Configurator and Blackbox Explorer?
I have picked up an older quad to get some experience in FPV flying. I'm not sure of the make or model of the quad - it doesn't seem to have a label. It does come with some printed instructions for setup and use, but these seem to be out-of-date.
The instructions say that I need Betaflight Configurator and Blackbox Explorer and that these should be downloaded from the Chrome Web Store. However, those apps don't appear to be available from the Chrome Web Store.
After a few Google searches, I found that they were removed following Google's announcement that they were going to be withdrawing support for all Chrome Apps. I also found an announcement that Betaflight would be developing standalone apps to replace the ones that were going to be removed from the Chrome Web Store. Unfortunately, those announcements don't say where the new standalone apps will be available from.
Now, I have searched, and I've found several sites that offer apps called 'Betaflight Configurator' and 'Blackbox Explorer', however, none seem to be official download sites (and several of them trigger safety warnings when I click on the links). Besides which, everyone knows that we shouldn't be downloading software these days unless it is from a trusted source.
So my question is simple.
Where is the official download site for 'Betaflight Configurator' and 'Blackbox Explorer'?
AI: Betaflight software is available from the Betaflight GitHub pages. These give the option of downloading pre-compiled binaries or the source code if you prefer to compile yourself.
Betaflight Configurator
Blackbox log viewer |
H: What is antenna gain?
As I understand it, generally, a higher gain antenna will result in a longer range and better reception for FPV flying. What is antenna gain? What makes a low-gain patch antenna different that a high-gain patch antenna?
AI: Gain, as a general term, is a measure of how large or strong something (a voltage, a radio wave, a sound wave, or whatever else) is relative to some baseline value of the thing being measured. A gain is a ratio: If a device takes a voltage on one end and makes it 20x larger (amplifies) it 20-fold, it has a gain of 20. In practice they are represented using decibels, a special unit that makes it easy to work with very large or small ratios. See the note at the end of this answer for more information about them.
Consequently, the gain of an antenna is the ratio of how much stronger the radio waves generated by the antenna are, relative to those generated by a standard "reference antenna" when fed by the same signal.
This reference antenna used as a baseline is considered to have a gain of 0 dB, or 1:1 (equal to itself).
The reference antenna is usually one of two types: An ideal isotropic antenna, which radiates equally in all directions with zero losses, or a dipole antenna. To indicate which one is used as the baseline, a letter is added to the end: dBi represents gain relative to an isotropic antenna, and dBd relative to a dipole.
The dipole itself has a gain of 2.15 dBi (and 0 dBd), so to convert a dBi gain to a dBd gain you subtract 2.15 from it, or add the same number to convert the other way around.
Symmetry
Every antenna receives the same way as it transmits, so an antenna's reception gain (how strong of an electric signal is generated in it by a radio wave, relative to the chosen reference antenna) is always the same as its transmission gain.
An antenna with 3 dB (2x) gain in a certain direction will transmit 2x the power in that direction, but also radio waves coming from this direction will generate 2x stronger signals for a connected receiver to detect.
If an antenna's gain is 13 dBd (a 20:1 ratio), its signal will be 20 times as strong as a dipole's (and its reception will be 20x stronger as well)! Wonderful, right?
Well, there is a caveat to high gain, and it basically boils down to: There ain't no such thing as a free lunch.
Gain and directionality
True isotropic antennae do not exist in the real world, i.e. no real antenna radiates equally strong in all directions. There are directions in which it will radiate the strongest, and others in which it doesn't radiate at all. So the gain of a real antenna is not the same in all directions either: in some it is stronger, in some it is weaker. The easiest way to show this is a graph showing the antenna’s gain in every direction around the antenna. That graph is called a radiation pattern and looks like this:
The bold line represents the gain: the further it is from the center, the bigger the gain. Above is the radiation pattern of a directional antenna: the gain in one direction is a lot more than in other directions.
So when we speak of an antenna's gain, we really mean its gain in a certain direction. And that direction is usually the one in which the antenna's gain is the strongest.
Also, you can't get more out of an antenna than you put into it. The sum of all power radiated in all directions is always equal to the power that goes in (Minus a small percentage of losses); Antennae create gain by radiating this power such that the created waves add up in the preferred direction and cancel in others.
So if an antenna has a higher than baseline (positive) gain in some direction, you pay for that by having a negative gain in other directions. Gain only focuses power — it does not create power.
For our imaginary 13 dBd antenna it means that only a small sector will get this much gain, and all the other directions will have almost zero radiated power to make up for it.
So gain is not only the measure of how well an antenna receives or transmits, it's also a measure of the antenna's directivity: If the antenna focuses all of its power in a tight cone, it will have a huge gain within that cone, and a huge gain rating on the box... But its gain outside of that cone will be almost nonexistent. So when you are choosing a directional antenna, the gain is also an indication how directional it really is. Lower-gain patch antennae will give you a soft, forgiving cone but lower gain in it, while high-gain directionals will have a very tight zone in which they could transmit or receive at all, but within it they will be super powerful.
Omnidirectional antennae (which, as you now know, are never truly omnidirectional) have a radiation pattern that's more or less shaped like a donut:
They have an equal (and positive) gain in any direction perpendicular to the antenna, which gets lower as the direction gets closer to parallel to the antenna. These antennae also have their own kind of directivity: if you mount the antenna vertically, the "horizontal" gain will be the same in any direction, but it can be higher or lower relative to the "more vertical" directions, making the donut flatter. In other words, the antenna can prioritize gain towards the horizon versus overhead gain more or less.
A note on decibels
In many engineering fields ratios can easily get extremely large or extremely minuscule and tend to multiply a lot. Radio is one of the most prominent of those. At the input to a receiver, signals are frequently
smaller than one ten-billionth of a watt. When they come out of a transmitter, they’re often measured in kilowatts! Antennas, propagation and electronic circuits change signal strengths by many factors of ten.
To manage these vast differences in value, engineers measure ratios in decibels, or dB, which represent the ratio of
two quantities as a power of 10. The formula for computing decibels is:
dB = 10 * log_10 (ratio)
This is a logarithmic unit, meaning that when two ratios are multiplied, their representations in dB are simply added up: 10 decibels represent a ratio of 10:1; 20 dB is 1010=100:1, and 30dB is 1010*10=1000:1.
Positive values of dB mean the ratio is greater than 1 and negative values of dB indicate a ratio of less than 1: -10 dB represents a ratio of 1/10, and 40dB is 1/10000.
Here's a quick cheat sheet of dB to actual ratio for numbers smaller than 10:
1dB corresponds to about 1.25:1
3dB is almost exactly 2:1 (this is the most important one to remember)
7dB ~= 5:1
10dB is 10:1 (exactly)
For everything else, you just add up the numbers you know:
6dB (=3dB+3dB) is ~ 4(=2*2):1, and 9dB is ~ 8:1
13 dB is 10 dB + 3 dB, so 10*2=20:1.
46 dB is 40 dB + 6 dB = 10^4 * 4 = 40000:1
15 dB is 10dB + 5dB; and 5 dB is somewhere between 3dB and 6dB (2 and 4), so it's probably three point something. Thus our guess would be 15dB is somewhere in the 30-35 to 1 range. |
H: Are there any brushed outrunner motors?
The most common motors on drones are brushless outrunner motors. I´ve also seen some brushless inrunner motors. Are there any brushed outrunner motors? If so, why are they so uncommon?
AI: The difference between outrunner and inrunner BLDC (brushless DC) motors is that an outrunner's rotor is outside the stator while an inrunner's rotor is inside the stator.
(cit.)
In general, outrunners have more torque and rotate slower than inrunners, which usually have less torque and rotate significantly quicker. The two different designs are possible because it is relatively easy to conceptualize how to flip the order of the stator and rotor within the motor due to the fact that no mechanical commutation is necessary, unlike in a brushed motor.
Almost all brushed DC motors would be classified as inrunners and very few brushed outrunner designs exist, as you note. The Wikipedia page for Brushed DC motors makes no reference to an "outrunner" brushed motor and almost no search results appear for them.
I'm not a designer of electric motors, but I have a theory for why this might be the case: the usefulness of brushed motors is mostly because they are inrunners.
(cit.) (cit.)
The above images show "inrunner" brushed motors and the commutation mechanisms they require. If you were to make them into outrunners, the only difference they would have with brushless outrunners would be the swapped location of the coils/magnets. This setup would also increase the size of the commutation mechanism and forcing the brushes to be crammed inside the commutation ring, making it more complicated and susceptible to breaking. |
H: Why do most multirotors use outrunner brushless motors?
I've noticed that most every quadcopter drone I see uses outrunner BLDC motors like this:
Why is that? What unique advantages to outrunners have that make them better than inrunners for multirotors?
AI: The difference between outrunner and inrunner BLDC (brushless DC) motors is that an outrunner's rotor is outside the stator while an inrunner's rotor is inside the stator.
(cit.)
In general, outrunners create more torque and rotate slower than inrunners, which usually have less torque and rotate significantly quicker. The two different designs are possible because it is relatively easy to conceptualize how to flip the order of the stator and rotor within the motor due to the fact that no mechanical commutation is necessary, unlike in a brushed motor.
Whichever side of the motor (outside or inside) that is the stator is far thicker than the other because the orientation of the coils on the stator contributes a lot of depth. Outrunners trade increased torque for decreased rotation rate because the electromotive force between the magnets and coils acts roughly at the air gap between them, which is further from the center of the motor in an outrunner, resulting in an increased moment arm and more torque. (remember that τ = F x r where τ is torque in Nm, F is the force, and r is the distance from the rotational axis)
This increased torque is critical because the BLDC motors have no gearboxes between them and the propellers, which require decent amounts of torque to spin. In other systems, motors could use gearboxes to trade speed for torque, but the requirements of multirotors to be as efficient and lightweight as possible don't allow for them to be installed. |
H: What blocks an FPV video signal?
I am interested in long-range range FPV flying. What things block the video signal of a 5.8gHz video transmitter the most?
AI: Just about anything will block/interfere with radio signaling if there's enough of it in the path between the transmitter and receiver or in the immediate vicinity of them. (sometimes referrred to as the Fresnel Zone) However, these are some of the most notorious offenders:
Tight spaces with a lot of multipath interference
Concrete and brick structures
Bodies of water
Soil and earth
Large structures
Forests and large amounts of trees
Lots of human bodies
etc.
One could go on forever listing out different materials, but these are some of the more common items to encounter for FPV.
In general, the rule is to maintain as much line-of-sight as possible between the transmitter and receiver. This is true because obstacles will force the radio waves to take indirect paths, bouncing repeatedly off of stuff until it hits the receiver antenna. Multipath interference comes from this, because often many different (multi)paths will converge on the receiver at different times and cause interference with each other, distorting the image that your goggles/FPV receiver will pick up. |
H: How do you build and use a smoke stopper?
What is the right way to build and use a "smoke stopper" device to prevent a short or other improper wiring from damaging your electronics?
Is it different depending on what voltage you are using?
AI: There are different ways, but a common one is to put a light bulb in series with the positive battery lead.
This works because it will allow low currents through to power the flight controller, but if there is a surge in current from a short the bulb will light up and sap away the energy.
You need to make sure you have a light bulb rated for the voltage you intend to put through it - for example if you have a 3V light bulb and use it as a 6S smoke stopper, the filament will melt.
This guide by Joshua Bardwell is great to build a switchable smile stopper: https://youtu.be/I5a0TAmEwLE |
H: What is the performance difference between a brushless motor with a wider vs taller stator?
In the drone motor industry, there are a lot of variations in the stator sizes of brushless motors. There are several motors that have similar stator volume but one is wider and the other is taller. What are the inherent differences in performance between a drone motor that is wider stator vs one that has a taller stator with a similar stator volume? Would the stator shape influence which props it should use?
AI: The simple answer is "more width equals more torque".
More torque let's you drive a higher pitch or larger diameter prop effectively. Given the same size prop, it will drive it with more effectiveness. Added torque allows the prop to spin up or slow down faster, which ultimate results in a better flying quad because it can more quickly and accurately respond to your stick inputs.
In the miniquad community, this is the reason a lot of freestyle pilots trend toward wider motors on a 5" prop compared to racers. It provides a higher level of smoothness because of how it reacts.
Another effect of more width is more efficiency especially with big crafts that are targeting flight time. You'll see lots of the big (15" or larger) propeller quadcopters with very wide motors. For instance a 5010 stator size. High performance isn't usually the goal here so a wider stator allows them to drive the big prop without lots of excess weight and power that they don't need.
Oscar Liang also has a good concise explanation of different motor stator sizes here
This is an endurance quad I built years ago with the 5010 motors I mentioned. Just to give you an idea of the scale and the uses of a very wide motor. |
H: What is the difference between a patch and helical antenna?
I have seen both patch and helical antenna when shopping for video receiver antennae. All I know is that they are both directional antennae. Do these types of antennae have any inherent performance differences? (I´m talking specifically about 6-turn helical antennae compared to patch antennae)
AI: tl;dr: In terms of radio performance, they're almost identical if you compare similar-gain models, so choose based on dimensions, durability, maintainability and other practical considerations. If you're buying, patch is usually better simply in terms of size and toughness. However, consider DIYing a helical; it's cheaper, a nice project to do, and makes a very good antenna. Only buy a premade helical if you wanna do very long range flights and don't want to bother with making one.
If you only consider the strictly RF differences between these antenna classes, they are rather subtle. These indeed are both directional antennae, and the directivity for both classes can be varied in a rather wide range depending on the particular variant of the antenna. A helical antenna would get longer as its directivity increases, while a patch would get wider. One thing that may or may not be significant is that helical antennae tend to have a very symmetrical radiation pattern, i.e. a very round beam, while the radiation pattern of patch antennae tends to flare out slightly more to certain sides. This can be significant if you're using highly-directional versions and need to point your antenna to keep your aircraft inside its cone; for a helical antenna the gain reduction would be the same no matter in which direction the antenna is misaligned, it would only depend on how much it's misaligned. For a patch antenna the direction contributes as well, though maybe subtly.
Otherwise, there's not much to say. While in theory a helical antenna is slightly more efficient, in practice each antenna's efficiency would depend more on the design and fabrication of the particular antenna than on its class. Speaking of fabrication, I must also point out here that since patch antennae are PCBs, and helical antennae are likely at least in part assembled by hand, I would expect the characteristics of patches to be a bit more consistent antenna to antenna within the same model/manufacturer. You probably wouldn't notice either way.
The more significant characteristics are dimensions, endurance and ease of manufacture.
In the first two, patch antennae win by a long margin; they are both more compact and harder to damage in transportation or rough handling. For ease of manufacture... it depends. If you're looking at producing thousands of them, the patch also wins unequivocally, as it's just a PCB that can be automated and made very consistently and cheaply. If you need just one or two, however... The helical is far ahead. It's a very simple design that doesn't depend on things like copper thickness or the grade of material of the circuit board, its directivity can be easily set as needed by simply changing the number of turns and without recalculating anything, and it is very easy and cheap to manufacture at home using a minimum of parts and tools; the rarest of them is probably the coax connector and maybe the wire former (if you don't have plastic tubing of the right diameter or a 3D printer); the rest of the materials are probably already lying somewhere around your house.
So if I were to recommend, then:
If you're flying near yourself, don't want to worry about transporting/damaging it or want a premade antenna, go for a patch.
If you're willing to make one and/or you want to do very long range flights, AND you're okay with it being a bit bulky and less durable, helical is better. |
H: What is the typical glide ratio of Kline-Fogleman airfoils?
Kline-Fogleman (KFm) airfoils, despite their seeming contradiction with known principles of aerodynamics, seem to be very popular in RC modelling, and are known to have a peculiar stall behavior, with a gradual transition to high drag without loss of lift, unlike the sharp stall of traditional smooth airfoils.
There's little information I could find about how the stepped design affects the airfoil's aerodynamic efficiency, however. The design seems to be plenty good for powered fun-flyer planes; I've seen at least some KFm slope gliders, too, and a well-circulated picture (provided below) states that the KFm3 variant has "fantastic flight characteristics" and is good for sailplanes... But there are no hard numbers that I could find on just how good these airfoils are (or how good they can be) in terms of lift to drag (L/D) ratio.
Are there any known numbers for the typical and best case L/D values of aircraft with Kline-Fogleman (KFm) airfoils, and if so, what are they? How does this characteristic differ between variants of the airfoil design?
AI: This paper (AE-74-1054-1) from the University of Tennessee has a graph on page 15 showing the best they managed was 1:17 with the step on top and 1:8 with the step on the bottom but these were at a very specific angle of attack, and about half that was more typical.
The wind tunnel results show that for this new airfoil the lift/drag ratio is lower than for the flat plate, and the pressure data show that the airfoil derives its lift the same way as the inclined flat plate. This airfoil offers no discernable advantages over the conventional airfoil.
Anecdotally, that matches my experience with KFm gliders. They work about as well as a flat plate. Ok for a light-wieght park-flier with loads of thrust but no good for a glider. |
H: Can I salvage a 4in1 ESC?
I have a 4in1 Brushless ESC that only one ESC burned out on, but the rest should still be usable. Is there a way to salvage it and use a single ESC to replace the burned one or something? If so, how would I go about doing that?
AI: As ifconfig pointed out, the most common way to continue using a not entirely functional 4-in-1 is to solder a standalone ESC to substitute for the damaged one(s). Balance is not that much of an issue (that's what the I term is for), unless you're doing the highest performance flying, in which case you should just replace the whole thing.
Also, in order to not lose current sensing on the new ESC, it can pay to solder your new ESC's power leads directly to the VBAT power traces after the shunt resistor on the 4-in-1 (they are usually exposed and sometimes even have metal rails soldered to them). If you don't want to bother or aren't that good at soldering, you can usually make do without rewiring the extra ESC, and just adjust the current sensor multiplier. This isn't going to give you as precise a reading, but it's an okay approximation for gauging general current usage and deciding when to land, just don't rely on it too much. Multiply the number by 3/4 (or less, depending on how many surviving ESCs you have on the same board) for a first estimate, and maybe later make a finer adjustment by measuring the true mAh used from the pack vs. used mAh indicated in the OSD.
There are two more interesting ways to make use of a damaged 4-in-1, however.
The first one is similar to what ifconfig is suggesting, but instead of adding a standalone ESC, you add another 4-in-1 to the same stack, and wire it to the same flight controller (but to different motor pins, of course). For this you can even use another damaged ESC, as not all of the individual ESCs on the board may be used. This also gets rid of the balance problem if it bothers you somehow, and also lets you avoid clipping the wires of one of your motors shorter in order to accomodate the individual ESC.
The same caveat applies about current sensors as with an individual ESC, and it's going to be harder to wire the two power rails together, so you're probably stuck with using just one of the current sensors and adjusting the multiplier.
The second, and more advanced, is to just replace the damaged component on your ESC. It is usually one (or several) of the power transistors (FETs) of the ESC, and those can be easily replaced if you know how to use a heat gun. You'll need the replacements however. Most FETs used in popular 4-in-1s can be ordered, so it's a question of identifying the part number. |
H: Can circularly and linearly polarized antennae be used together for FPV?
I have a few spare antennae of mixed polarizations I'd like to be able to reuse for my FPV gear.
Is there anything I need to know about incompatible configurations of mismatched polarizations between my transmitting and receiving antennae?
AI: The compatibility of mixed polarity antennae depends greatly. For a little background in RF polarity, this diagram shows the difference between the four main types of antenna polarization available: (mixed/elliptical polarization do exist)
(cit.)
In general, it is best if the TX and RX antennae match in polarization, but some other combinations are possible while minimizing signal strength loss.
Linear → Linear
Linearly polarized antennae are interchangeable, as long as they are oriented in the same direction. Signal reception between linearly polarized antennae oriented with an angle between them of θ will fall off with a polarization loss factor (PLF) of PLF = cos^2 (θ) and reception will be zero when the antennae are perpendicular to one another.
Circular → Circular
As long as the circular polarization is identical (RHCP or LHCP) between the two antennae, no signal loss will be observed due to the polarization of the antennae. Signal strength isn't dependent on the angle between the orientations of the circularly polarized antennae. However, if you aren't using omnidirectional antennae (e.g. mushroom)¹ and instead have a directional antenna (e.g. patch, helical), you must point the directional antenna in the direction of the other antenna to have the most gain. (see "What is antenna gain?"). Within the beam width of the directional ciruclarly polarized antenna, orientation doesn't matter.
As pointed out by @FlashCactus, only circular → circular polarization matches benefit from the multipath interference reduction effect. This is because circularly polarized waves switch polarization when they bounce off of an obstruction (i.e. RHCP → LHCP and vice versa), so duplicate signals taking an odd number of bounces to reach the receiver will be ignored by the antenna. (they will be recieved as the opposite polarization with which they were transmitted)
For more details on how circular polarization works, I (and @FlashCactus) recommend having a look at this question: What is circular polarization in antennas?
¹: Omnidirectional antennae are also not truly omnidirectional; they have a region of low gain along their axis, and will transmit/receive poorly in that direction. It is best to face them sideways towards the other antenna for best reception. The same is true for linear antennae; they receive&transmit best from their sides and worst along the antenna.
Circular → Linear
Because a circularly polarized wave can also be represented by two 90° out-of-phase perpendicular linearly polarized waves, the linear antenna will receive with a signal strength reduction (PLF) of half (or -3dB). Signal strength isn't dependent on the angle between the orientations of the linearly polarized and circularly polarized antenna.
This configuration can be useful if you want to spectate someone who has the opposite transmitting antenna handedness from you (LHCP while you use RHCP, for example), or to scan the radio spectrum that might contain signals of different polarization (RHCP, LHCP or linear) without switching the antenna: A linear antenna will receive both RHCP and LHCP signals equally well.
Linear → Circular
Likewise from before, because the circularly polarized antenna is built to receive both perpendicular components of the circularly polarized wave, it will receive a linearly polarized wave with a signal strength reduction (PLF) of half (-3dB). Signal strength isn't dependent on the angle between the orientations of the linearly polarized and circularly polarized antenna. As with the opposite configuration, RHCP and LHCP antennae will receive linearly polarized signals equally well.
This configuration can be commonly seen in the case of micro-quads like Tinywhoops which only come with linearly polarized transmitter antennae. Here, the orientation-agnostic benefits of receiving a linearly polarized signal with a circularly polarized antenna (and the convenience of not replacing the antennae on your goggles) are often worth the signal strength reduction. |
H: Can I use LiHV batteries as normal batteries?
I have a small drone and the only batteries I can find that fit it are LiHV batteries. Can I use LiHV batteries like normal LiPo batteries? Can I just simply charge a LiHV battery to 4.2v and fly with it?
AI: Yes, you can. The primary difference between LiHV and LiPo batteries is the ability to change them to ~4.35 V/cell instead of 4.20 V/cell with a nominal cell voltage of 3.8 V instead of 3.7 V.
Just like how there's nothing stopping you from only charging your LiPos to 4.1 V/cell instead of their rated full charge @ 4.20 V/cell, there's nothing wrong with charging LiHVs to a "full" charge below their rating. |
H: How to determine the correct specification of servo for a control surface
Servos come in a large range of sizes, torque values, etc. and the servo to use depends on a number of factors such as control surface size, aircraft speed and desired manoeuvrability.
While there is some intuitive correlation (as an aircraft gets larger, usually so do the servos), is there a way to calculate or determine the 'right' servo to use, sufficient to safely and reliably control the aircraft while keeping the 'downsides' (cost, weight, power consumption) as low as practical?
AI: Most forces in aerodynamics are proportional to area, speed squared, air density and a 'coefficient' that describes how efficient your object is. There's also usually a 1/2 for obscure theoretical reasons.
If you work in metric, the density of air at sea level is basically 1, which takes that out of the equation.
The maximum lift coefficient of an average wing is roughly 1. The drag coefficient of a non-aerodynamic object is also (very) roughly 1 (see link for examples), so for a first approximation, we'll use 1.
Now you've got to guess the maximum speed of your model, maybe by multiplying the motor Kv, battery voltage and prop pitch.
That should give you the maximum force on the control surface. We've no idea how it's distributed but we'll assume it's in the middle. Multiply the force by half the chord to get the torque.
Then allow for differences in the length of control horns. If they're the same, the servo needs the calculated torque. If the servo horn is half as long as the control surface horn, the servo will only need half the torque.
Finally, double or triple that value to give yourself a safety factor.
Alternately, just copy a similar model.
Then when you test fly, don't try any high-speed dives until after you'd tried a level full speed pass. If the controls feel sluggish at speed, you need larger servos. |
H: How do I calculate thrust for a quadrocopter?
I am designing a quadrocopter style aircraft that uses a 20 inch propeller 1.625 inches in width and has a pitch of 8 inches. How do I calculate static lift / thrust and the dynamic thrust / lift forces when it would be moving in a direction (not diagonal in an upward or downward).
Thank you.
AI: The usual way to calculate exact thrust is actually experimentally, through testing on a thrust stand. There are countless factors that may influence the performance of your particular motor and propeller combination, some of which are hard to measure and quantify, so the exact number has to be found out just by testing it.
That said, if you only need a rough ballpark, testing your particular combination is not required; you can look up test results for other motors and props of the size you want. 20 inches is very uncommon, so the data may be scarce, though; if you don't find any, doing it yourself is the best bet.
As for dynamic thrust, it is even harder to predict, especially as it depends on the quadcopter's configuration in addition to its attitude and speed; if you want precise enough numbers, you'd probably have to employ either a wind tunnel or a numerical simulation (which is not that unreasonable of a cost for the size of drone you're planning). That said, I'm not entirely sure you actually need it, it's usually sufficient to ensure that the drone's static thrust to weight ratio is high enough (2.5+ is a good number for slow flyers such as camera drones; 4 is good for sporty flying, 8 is good for competitive flying). |
H: Would the FAA's proposed Remote ID really ground older drones?
The FAA has proposed new rules regarding drones, particularly Remote ID
Remote ID would assist the FAA, law enforcement, and Federal security agencies when a UAS appears to be flying in an unsafe manner or where the drone is not allowed to fly.
The development of Remote ID builds on the framework established by the small UAS registration rule (PDF) and the LAANC capability to lay the foundation of an Unmanned Aircraft System Traffic Management System (UTM) that is scalable to the national airspace.
Criticism has been harsh
“Casual drone users would have to establish, maintain, and renew subscriptions just to fly occasionally in their backyards. School programs that use drones may decide the costs are just too high to continue. A gift of a drone on Christmas would saddle your recipient with endless monthly fees. And connecting all drones to the internet would create new cybersecurity vulnerabilities.”
Also
And then there are the technical barriers to compliance. Schulman points out that “thousands of drones and radio-controlled aircraft currently on the market have no means for internet connection and would be grounded.”
Would this regulation really ground all existing drones?
AI: The FPV Freedom Coalition has an excellent summary page at this link.
To sum up the answer to your question as simply as I understand it: older drones that are not able to broadcast their information will NOT be grounded, however they will be required to only fly within FRIAs (FAA Recognised Identification Areas).
Under the current proposal, after one year no new FRIAs may be registered, so as they disappear over time it may become more difficult to legally fly non-compliant aircraft.
I am not a legal expert - if anyone feels my understanding is incorrect then please do let me know. |
H: How to fix OSD displaying weird symbols
I upgraded from betaflight 3.X to betaflight 4.1.X and now my OSD displays weird symbols.
It seems to have replaced the crosshair. (The 3 L shapes in the center)
Expected result:
How can I fix it?
AI: I fixed it by re-uploading the font to the flight controller.
Some people report they need to power the quad with a LiPo for this to work. I did not need to.
Go to Betaflight's "OSD" tab
Click "Font Manager"
Click "Upload Font"
I'm now back with a normal crosshair.
As @3k pointed out,
The reason for this is that the character set has changed between versions so it has to be updated on the copter. |
H: What is a "mushroom antenna"?
In Can circularly and linearly polarized antennae be used together for FPV? I read about a "mushroom antenna". While I have very little experience with FPV drones I am generally experienced in radios and I had not heard of such a thing, so my curiosity was piqued.
Searching the cybernets, I'm able to find a great many of these antennas, largely low cost devices aimed at the FPV market. But I was unable to find any engineering information, such as the details of their internal construction or radiation pattern.
So what precisely are these antennas? Do they have a particular construction or will any antenna inside a mushroom-shaped radome do? Are there any available technical documents which show their radiation patterns, either through simulation or empirical measurements?
AI: A "mushroom" is just a clover-leaf antenna. Generally they have a plastic cover that makes them look like a mushroom, hence the name. |
H: How to program drones that have old flight controllers?
I have a few components of drones like some old FCs and old ESCs and I don't want them to go to waste. Is there any way to configure a drone that I built with those parts, as I don't think the FCs are capable of running BetaFlight. (are there any really simplistic, light things that the FC can run instead of BetaFlight?)
AI: You can always run an older version of betaflight. Also, if you have older F3 controllers you may also like to like to look at https://github.com/spatzengr/betaflight/releases which are maintained by UAV Tech.
I have used these on some older F3 boards and it breathes new life into these old boards. |
H: How to charge LiPo batteries in series?
Is there any way to use my main charger, which can charge 2-6s batteries, to safely charge multiple 1s batteries in series? (assuming all of the batteries are the same capacity)
How would I go about doing this?
AI: Huh. I never thought about this before, but charging identical LiPo batteries in series with one another seems logical enough. In fact, here's an article which discusses how to do it, which I'll summarize here.
Prerequisite requirements:
The charger must support the series battery (e.g. for 2x 4s batteries, the charger must work with at least 8s)
You must create a balance lead adapter (and separate main discharge lead adapter) that combines the leads from the batteries into one. The highest voltage cell on one battery will have the same balance connector pin as the ground wire in the next battery's balance lead. (graphic below shows this in more detail)
All batteries MUST be the same capacity, but not necessarily the same cell count. (e.g. not 1s 1000 mAh and 1s 1500 mAh, but 1s 1000 mAh and 4s 1000 mAh is fine)
All batteries MUST have per-cell voltages that are close to one another. A difference of 0.05 V is usually okay.
Advantages
Time savings from charging all at once and hooking up batteries fewer times
Can allow for faster batch charging than parallel charging if the charger's power limit is less of a bottleneck than the current limit
Unlike parallel charging, each individual cell is monitored and balanced separately by the charger
Disadvantages/Risks
If something were to go wrong during the charge cycle it would effect multiple packs. (e.g. an internal cell short in one pack could light all packs on fire)
All batteries MUST be properly connected to both the main discharge lead adapter and balance connector adapter, (and connected in the right order) or funky stuff like short circuits and fires could happen!
Can be a slower batch charging method than parallel charging if the charger's power limit is more of a bottleneck than the current limit |
H: What is the point of a dual-gyro setup for a FC?
When looking for a flight controller for a drone build, I have seen some FCs with dual-gyros. What is the purpose of having two gyros on a FC? (Are there any advantages or disadvantages)
AI: A major advantage is redundancy, so that the aircraft can continue flying if one fails. It is also common to see multiple GNSS (e.g. GPS) receivers, and sometimes even a redundant flight controller.
Of course, the problem with only two is that the software can't necessarily tell which of them has failed; 'at least three' is common for high resilience applications as it is much less likely for two failures at the same time (barring external factors, such as a power spike.)
Going further, you can also use different brands and/or technologies to remove the risk of a design or manufacturing flaw causing them all to fail at the same time.
The typical disadvantages apply - increased cost, weight and power consumption - but also software complexity increases as you need to have a method for handling the potentially erroneous data. |
H: Quality of transmitted image and electrical problems
There is a question already regarding a flickering OSD, but I wonder how other image quality problems relate to electrical problems. What's the first thing one has to look for when the transmitted image is jumping or features vertical running lines or the quality of the image seemingly depends on throttle value? What are common wiring strategies to avoid these kinds of problems and what are their respective root cause?
What I usually do is power the VTX from BEC/ESC (or directly from battery if it is rated for it) and power the camera from the VTX 5V out and braid the wires, but I think there must be more to know about image transmission issues.
AI: There’s a lot to unpack here, so I’m going to give a general kind of advice that should be helpful for anyone trying to get cleaner video:
Electrical Power
There are two main aspect to the image transmission: the camera and the VTX.
Whenever you have noise, the first step would be to increase power filtering as much as possible.
The easiest way to do this is to add a capacitor to the battery pads to filter out the voltage spikes.
If that doesn’t work, try powering your VTX from a BEC on your flight controller instead of VBAT (if that’s what you already have).
Also try powering your camera from a BEC on your VTX if it has one.
Then try adding a common ground between the camera and the VTX to avoid what is called a ground loop.
There are other sources of power noise, which could include oscillations that cause voltage spikes in the motors.
Antennas
The antenna you use also has a big impact on video.
The best way to ensure good video link quality is to have two circularly polarised antennas with the same polarisation, for example RHCP with RHCP and LHCP with LHCP.
You can also use a patch antenna to increase the reception of your goggles at the expense of the number of directions from which you can receive a signal.
VTX
Have you ever powered on your VTX without an antenna? This can sometimes cause the VTX to become damaged.
If you have a spare VTX, try using that and see if quality improves.
VTX Settings
If you’re flying in a wide area, you can try increasing your VTX power (as long as it is legal).
If you’re flying in a tight space like a bando, sometimes having a higher power output can actually make the video signal worse due to multipath interference. If you experience that, you may want to try lowering the power output.
Frequency
Make sure your goggles are on exactly the same frequency as your video transmitter.
People often use the auto-scan function on their goggles, however this is known to be inaccurate and often goes to a close channel, but not the exact one.
The wrong frequency will introduce static, but it is unlikely to create the lines you describe.
It is also possible that lines may be caused by RF interference from WiFi, power lines etc. You may be able to get around this by changing your frequency. |
H: Is voltage sag safe if the voltage isn't too low?
I know that a liPo cell should never be below 3.0 volts, but can voltage sag during high throttle maneuvers damage the battery excessively even if the voltage it not below that level?
And if that is the case; should you try to limit how much the voltage sags by getting a battery with a higher C-rating, or will the difference be negligible if you go from, for example, 75 C to 100 C on a 1500 mAh battery.
AI: Yes, voltage sag is perfectly normal and safe for the battery, so long as it remains above the recommended minimum voltage levels.
The C rating is important as the construction of a cell affects how quickly it can provide current. The internal surface area of the positive and negative terminals is related to the current it can provide - a larger surface area lowers the internal resistance and this causes less heating when discharging. This is why higher C packs are bulkier. |
H: Are there any extremely small brushless drone motors?
I have seen many tiny brushed drones, about an inch from motor to motor, and was wondering whether it would be possible to create a brushless drone that small. Are there any brushless motors available that are extremely small, ones that could fit on the size of drone below? And is there anything else to consider if making a drone so small?
(I realize that you could put oversized motors on a small drone but I am asking about motors that would be proportionally normal)
AI: Theoretically, I don’t see why we couldn’t make current motors even smaller than they are today - we already have brushless motors with stators less than 10mm across (for example these 0802 motors), and we could change the format by using inrunner motors instead. However there are certain factors that we need to consider.
The first of these is that we can’t just have the motors - we also need the ESC boards. This is either done with a 4-in-1 ESC or 4 individual ESCs. This adds complexity, weight, size and heat buildup.
We must also consider whether or not these negatives outweigh the positives. This is up to personal opinion, and in some instances it may well be worth it, however with miniaturisation comes increases manufacturing complexity with smaller tolerances.
These are all important factors to consider: is it possible and is it worth it.
I believe it is possible, however finding enough demand may be a limiting factor. |
H: Does active braking help protect propellers from damage?
As far as I know with active braking option enabled in BLHeli32 the speed controller will counteract the free spinning of the rotor according to throttle value hence making it slow down quicker when needed. Could this help protect propellers upon crash?
AI: No matter how quickly you slow down the propellers after an impact with the ground, much of the damage actually comes from the impact directly into the ground and the force from the mass of the quad, so the speed of the props shouldn’t make too much of a difference.
If you mean the slowing down the props after it’s on the ground would save them, it may prevent further damage to the props, however the current draw if the props get caught in something could easily fry an ESC so it is likely more economical to sacrifice the props.
I generally go by the rule that if I crash, disarm as fast as possible. This stops me from burning ESCs as I’m usually disarmed before I hit the ground, though this comes with the negative that i can’t recover after a crash because I’ve disarmed. |
H: At what current should I charge a LiPo battery?
I have several different LiPo batteries which I use with my drones, many of them are different voltages and different capacities. How do I know at what current I should charge my drone LiPo batteries?
AI: Charging Lithium batteries is a far more delicate process than discharging them because of the complex chemical processes involved. Batteries that are rated for tens of "c"s of discharge rate are usually only rated for 1-2 "c"s of charging rate. Standard charging rates are 1c for regular speed and 2c for fast charging, with 2c damaging the battery more.
C-ratings are an artificial marketing term that doesn't really help very much without being converted using this formula: Charging Current (amps) = C-rating * Battery Capacity (amp-hours) where one amp-hour (Ah) is equal to 1000 milli-amp-hours (mAh).
So, for example:
1500 mAh battery charging @ 1c = 1.5 A charging current
2000 mAh battery charging @ 1c = 2.0 A charging current
2000 mAh battery charging @ 2c = 4.0 A charging current
2000 mAh battery charging @ 0.5c = 1.0 A charging current
Charging at higher currents (higher c-ratings) is more damaging to the battery's cells and is more likely to cause complications like fires and explosions while charging. The opposite is true for charging at lower currents. It is hardly ever recommended to charge at more than 2c, and staying as close as possible to 1c is always recommended for safety and battery longevity. |
H: What does the TVL rating mean for FPV cameras?
I see listings for analog FPV cameras like this one which have ratings in units of TVL. (e.g. 1000 TVL or 1200 TVL) What is TVL?
AI: TVL (TeleVision Lines) is a measurement of the "resolution" of an analog camera. Digital video systems use pixel resolution to specify how many pixels wide and tall the image is (e.g. 1080p = 1920 pixels wide by 1080 pixels tall), but analog video systems don't technically have pixels so there has to be some other way to represent their resolution capabilities.
(cit.)
The horizontal resolution power of analog video (TVL) measures how many distinct vertical bars can be depicted by the device (either a camera or display screen) across a horizontal length equal to the height of the picture. The example diagram above shows analog video with 6 TVL.
Cameras with higher TVL ratings will be able to capture smaller details than other cameras, although this is also dependent on the capabilities of the other equipment in between the camera and your FPV goggles or screen. |
H: How to mount XM+ receiver antennas?
I like to use XM+ receivers on many drones as they seem to work well and are small/light. What is the best angle and position to mount the antennas of an XM+ receiver in order to get the best signal?
I have often seen XM+ antennas mounted at a 90º from one another on the back of a quad. Is this a good configuration or are there other configurations that have better reception?
AI: TL;DR: From purely a range consideration the 90 degree mounting is the best because of the orientations your quad might see. You'll want to get the antennas as far away from the frame as you can so that the frame can never block at least on antenna from seeing your transmitter.
When you are considering ways to mount your antennas on a miniquad however there isn't one best way to mount them. Range, quad orientation and durability all play a part in what will work best for you. That said there are two things you should know to understand about antenna placement and why the 90 setup is recommended for range.
The reason for two antennas.
The XM+ antennas both have the same function. The receiver simply compares their signal strength and picks which one is best. This lets you place them in different orientations so that depending on your orientation on antenna or the other will have adequate signal.
The radiation pattern.
Generally the monopole antenna has it's best signal reception at a direction that's perpendicular to the antenna itself. Conversely it suffers from pretty bad reception in the top and bottom directions. This image shows the typical radiation pattern. Imagine the wire antenna standing straight up inside this donut. The red directions have good reception and the green are where it is bad.
Now, since you have two antennas you can see how rotating the second one by 90 degrees would cover the deadspots of the first antenna.
These two orientations make for good coverage in almost any orientation. However, it's not perfect, those donuts are pretty flat. Mounting both antennas in a more upright 'V' orientation could provide a lot more even coverage, but only if you don't plan on doing something like diving straight down.
With all that said, realize that those nice donut patterns can be blocked by your frame if they are placed in such a way that the frame can come inbetween you and the antenna. You can see how this would happen in Paul's example. Not to say that's a bad way to do it. I do it that way often. For typical park rages it still gives you that 90 degree orientation and will protect your antennas from prop strikes and crashes more effectively. For extended ranges though, one antenna sticking out the top and one out the back will give you the best range. |
H: When I power up my flight controller and ESC's, I hear a series of beeps. What do all of the beeps mean?
How can you use the series of beeps you hear when powering up to diagnose issues with your equipment? Should all of the beeps be synchronized or is it ok if they are slightly off? Are there different patterns you might hear and if so, what do they all mean?
AI: So normal startup sequence is three short beeps followed by two long beeps with different tonality.
First three beeps means that ESC is powered and activated.
Then if the throttle signal is detect goes one long low tone beep.
Then if throttle is zero goes one long high tone beep. This signal means the end of the start sequence and ESC is ready to run.
Here is diagram of normal boot sequence beeps:
There are manuals for both BlHeli_S and BlHeli_32 and they have a sections about sound sequences and what they mean.
Links:
BLHeli_32 manual ARM Rev32
BLHeli_S manual SiLabs Rev16
Regarding the slight de-sync of startup tones it looks like this is not a problem and just something to do with Betaflight boot process and happens only with Bi-directional DShot enabled: https://github.com/betaflight/betaflight/issues/9103
Most likely this is caused by:
Some ESC's first entering boot mode because the signal line from the FC is not readily booted and doesn't provide stable signal level before the ESC is booting.
And it can be "fixed" if you first power-on the Flight Controller and then the ESCs: https://github.com/betaflight/betaflight/issues/9103#issuecomment-546684302 |
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